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Psychometric Properties of the Symptom Questionnaire--48 in Adults with Mild Intellectual Disability or Borderline Intellectual Functioning in Mental Health Care

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Title: Psychometric Properties of the Symptom Questionnaire--48 in Adults with Mild Intellectual Disability or Borderline Intellectual Functioning in Mental Health Care
Language: English
Authors: Renate A. van der Heijden, Kim van Zutven, Inge P. C. Verhagen, Renate Venhorst, Jeanet G. Nieuwenhuis, Hubert P. L. M. Korzilius, Paul T. van der Heijden, Robert Didden
Source: Journal of Mental Health Research in Intellectual Disabilities. 2025 18(3):265-279.
Availability: Routledge. Available from: Taylor & Francis, Ltd. 530 Walnut Street Suite 850, Philadelphia, PA 19106. Tel: 800-354-1420; Tel: 215-625-8900; Fax: 215-207-0050; Web site: http://www.tandf.co.uk/journals
Peer Reviewed: Y
Page Count: 15
Publication Date: 2025
Document Type: Journal Articles
Reports - Research
Descriptors: Psychometrics, Questionnaires, Adults, Mild Intellectual Disability, Mental Health, Test Validity, Test Reliability, Foreign Countries, Symptoms (Individual Disorders)
Geographic Terms: Netherlands
DOI: 10.1080/19315864.2024.2416697
ISSN: 1931-5864
1931-5872
Abstract: Introduction: Increasingly more self-report measures of psychological distress are used as screening tools in mental health care for treatment planning and routing outcome monitoring. Research on the psychometric properties and utility of these measures in individuals with mild intellectual disability or borderline intellectual functioning (MID-BIF) are limited, even though this target group accounts for a large proportion of individuals treated in mental health care services. The aim of the present study was to explore the psychometric properties of the SQ-48, a self-report on psychological distress, when used in adults with MID-BIF. Methods: The SQ-48 was administered to 213 patients of two specialist mental health services for MID-BIF in the Netherlands. A second administration took place after three weeks in a test-retest design (N = 24). Results: The SQ-48 has adequate internal consistency, discriminant validity, test-retest reliability, and factor structure when used in adults with MID-BIF. Conclusion: This study provides preliminary evidence that the limitations in intellectual and adaptive functioning in people with MID-BIF do not influence the reliability and validity of the SQ-48 and can be used reliably in this population.
Abstractor: As Provided
Entry Date: 2026
Accession Number: EJ1502931
Database: ERIC
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  Value: <anid>AN0186344827;[5ew6]01jul.25;2025Jul04.07:15;v2.2.500</anid> <title id="AN0186344827-1">Psychometric Properties of the Symptom Questionnaire-48 in Adults with Mild Intellectual Disability or Borderline Intellectual Functioning in Mental Health Care </title> <p>Introduction: Increasingly more self-report measures of psychological distress are used as screening tools in mental health care for treatment planning and routing outcome monitoring. Research on the psychometric properties and utility of these measures in individuals with mild intellectual disability or borderline intellectual functioning (MID-BIF) are limited, even though this target group accounts for a large proportion of individuals treated in mental health care services. The aim of the present study was to explore the psychometric properties of the SQ-48, a self-report on psychological distress, when used in adults with MID-BIF. Methods: The SQ-48 was administered to 213 patients of two specialist mental health services for MID-BIF in the Netherlands. A second administration took place after three weeks in a test–retest design (N = 24). Results: The SQ-48 has adequate internal consistency, discriminant validity, test–retest reliability, and factor structure when used in adults with MID-BIF. Conclusion: This study provides preliminary evidence that the limitations in intellectual and adaptive functioning in people with MID-BIF do not influence the reliability and validity of the SQ-48 and can be used reliably in this population.</p> <p>Keywords: Psychological distress; psychometric properties; routine outcome monitoring; mild intellectual disability; borderline intellectual functioning</p> <p>An increasing number of measures of psychological distress are used as screening tools in mental health care settings, which are important for treatment planning and measuring treatment outcome (e.g. Barkham et al., [<reflink idref="bib3" id="ref1">3</reflink>]; Boswell et al., [<reflink idref="bib6" id="ref2">6</reflink>]). Psychological distress, also called symptom distress, is a state of emotional discomfort and a reaction to stressors resulting in a mixture of psychological symptoms, such as poor self-esteem, hopelessness, dread, and somatic symptoms. It adversely affects social functioning and day-to-day living (Drapeau et al., [<reflink idref="bib14" id="ref3">14</reflink>]). Multiple self-report measures of psychological distress are available, and they all broadly assess nonspecific psychological symptoms and symptom severity (Batterham et al., [<reflink idref="bib5" id="ref4">5</reflink>]).</p> <p>Despite these numerous options, research on the psychometric properties and utility of these measures in individuals with mild intellectual disabilities or borderline intellectual functioning (MID-BIF) is limited, though this target group accounts for a large proportion of individuals treated in mental health care services (Nieuwenhuis et al., [<reflink idref="bib21" id="ref5">21</reflink>]; Seelen de Lang et al., [<reflink idref="bib22" id="ref6">22</reflink>]). The characteristics of a mild intellectual disability (MID) are mild impairments in intellectual (IQ ± 50–70) and adaptive functioning, with an onset during the developmental period (American Psychiatric Association, [<reflink idref="bib1" id="ref7">1</reflink>]). Borderline intellectual functioning (BIF) signifies problems associated with below-average intellectual abilities, a higher probability of clinical treatment, and adverse effects on an individual's treatment process or prognosis (APA, [<reflink idref="bib1" id="ref8">1</reflink>]). Due to some similarities in support needs (e.g., simplified language use and repeated (visual) presentation of information), people with BIF and those with MID are combined into a MID-BIF target group in the mental health care in the Netherlands.</p> <p>A small number of studies show that measures for psychological distress have good psychometric properties when used in individuals with MID-BIF (e.g., Barrowcliff et al., [<reflink idref="bib4" id="ref9">4</reflink>]; [<reflink idref="bib12" id="ref10">12</reflink>]; Kellett et al., [<reflink idref="bib18" id="ref11">18</reflink>]; Vlissides et al., [<reflink idref="bib24" id="ref12">24</reflink>]; Wieland et al., [<reflink idref="bib26" id="ref13">26</reflink>]). The 48-item Symptom Questionnaire (SQ-48; I. Carlier et al., [<reflink idref="bib9" id="ref14">9</reflink>]) distinguishes itself from other measures of psychological distress by adding the constructs of vitality/optimism and work performance. Adding these constructs aligns with the increasing attention for positive mental health and recovery in various domains within mental health settings (e.g. Winsper et al., [<reflink idref="bib27" id="ref15">27</reflink>]). Furthermore, the SQ-48 is publicly available for clinicians and researchers, which is a great advantage when used in Routine Outcome Monitoring (ROM) or scientific studies. In addition, the psychometric properties of the SQ-48 are well investigated in clinical and non-clinical samples and showed good internal consistency, validity, test–retest reliability, and responsiveness to therapeutic change (I. Carlier et al., [<reflink idref="bib9" id="ref16">9</reflink>]; I. V. E. Carlier et al., [<reflink idref="bib10" id="ref17">10</reflink>]). Lastly, in the Netherlands, the SQ-48 is a measure utilized in many mental health settings for a large variety of mental health disorders as recommended by the national quality standards for mental health practice (Alliantie Kwaliteit Geestelijke Gezondheidszorg, [<reflink idref="bib15" id="ref18">15</reflink>]). Being able to use the same instruments for people with different levels of intelligence (from high intelligence to intellectual disability) has multiple advantages in research and clinical practice. For example, in research, the treatment effects can be compared between groups of different levels of intelligence, to better determine the influence of intelligence and other factors. Additionally, the use of the same instruments can reduce stigmatization and improve generally applied protocols (e.g., Cooper et al., [<reflink idref="bib12" id="ref19">12</reflink>]).</p> <p>Notwithstanding the benefits of the SQ-48, its psychometric properties have not been explored in patients with MID-BIF. Therefore, the aim of the present study was to investigate the psychometric properties of the SQ-48 when used in adults with MID-BIF in a specialized mental health setting and explore the level of psychological distress in this target group. The purpose of the current study is to instigate research on the utility of the SQ-48 in treatment planning and evaluation of people with MID-BIF.</p> <hd id="AN0186344827-2">Method</hd> <p></p> <hd id="AN0186344827-3">Setting and Participants</hd> <p>Data were collected from a sample of adults with MID-BIF registered at two mental health care services specialized in the assessment and treatment of mental disorders in people with MID-BIF in the Netherlands. Both services provide outpatient care, daycare, and inpatient treatment.</p> <p>Participants were 213 adults with MID-BIF and comorbid mental disorders, of whom 134 (62.9%) were self-identified females. The age of participants ranged between 18 and 72 years (<emph>M</emph> = 38.2 years; <emph>SD</emph> = 13.6). Of the total sample, 105 participants (49.3%) were classified with mild intellectual disability and 91 participants (42.7%) with borderline intellectual functioning. Table 1 presents the frequencies and percentages of the primary diagnoses. Of the participants, 142 (66.7%) had more than one comorbid mental disorder. With regard to the setting: 89 (42.0%) were outpatients, 64 (30.0%) were receiving day treatment, and 39 (18.0%) were inpatients. The remaining participants (<emph>n</emph> = 21, 10.0%) were referred to other services after the initial assessment.</p> <p>Table 1. Frequencies of primary diagnoses of mental health disorders.</p> <p> <ephtml> <table><thead><tr><td>DSM-5-TR classification</td><td>Frequency (N)</td><td>Percentage (%)</td></tr></thead><tbody><tr><td>Trauma- and stressor-related disorders</td><td>51</td><td>24</td></tr><tr><td>Depressive disorders</td><td>35</td><td>16</td></tr><tr><td>Anxiety disorders</td><td>28</td><td>13</td></tr><tr><td>Schizophrenia spectrum and other psychotic disorders</td><td>22</td><td>10</td></tr><tr><td>Autism spectrum disorder</td><td>20</td><td>9</td></tr><tr><td>Personality disorders</td><td>17</td><td>8</td></tr><tr><td>Bipolar disorders</td><td>8</td><td>4</td></tr><tr><td>Disruptive, impulse-control, and conduct disorders</td><td>3</td><td>1</td></tr><tr><td>Attention-deficit/hyperactivity disorder</td><td>2</td><td>1</td></tr><tr><td>No primary diagnosis*</td><td>27</td><td>13</td></tr><tr><td>Total</td><td>213</td><td>100.0</td></tr></tbody></table> </ephtml> </p> <p>1 *No primary diagnosis due to being referred to other services (<emph>N</emph> = 21) and system missing (<emph>N</emph> = 6).</p> <hd id="AN0186344827-4">Measure</hd> <p>The 48-item Symptom Questionnaire (SQ-48) consists of seven psychopathology subscales: depression (MOOD), anxiety (ANXI), somatic complaints (SOMA), social phobia (SOPH), agoraphobia (AGOR), aggression (AGGR), and cognitive problems (COGN). Two additional positive mental health subscales measure work/study performance (WORK) and vitality/optimism (VITA). The Dutch and English versions of the SQ-48 are freely available through the Leiden University Medical Center (LUMC) website (https://<ulink href="http://www.lumc.nl/afdelingen/psychiatrie/">www.lumc.nl/afdelingen/psychiatrie/</ulink>). In this study, the participants rated the Dutch version of the SQ-48 on each of the 48 items on a 5-point Likert scale ranging from never (0) to very often (<reflink idref="bib4" id="ref20">4</reflink>) referring to last week. The scores of items of each subscale were summed, with higher scores indicating more problems, symptoms, or distress, except for the subscale vitality/optimism, where a higher score indicates more vitality or optimism. The work/study functioning items were not scored if the respondent did not have work or some variation of social daycare. In addition, the scores of the seven psychopathology subscales, excluding the WORK and VITA scales, are summed to create a SQ-48 total score, ranging from 0 to 148, representing an overall level of psychological distress.</p> <p>The psychometric properties of the SQ-48 have been evaluated in several studies. In the first study, I. Carlier et al. ([<reflink idref="bib9" id="ref21">9</reflink>]) found that the nine-factor structure fitted well with the data in both the reference group and the patient group and the internal consistency was found to be adequate to excellent (<emph>α</emph> =.78–.98). In addition, the authors developed cutoff values with scores above the cutoff value suggesting mental health problems. In the second study, I. V. E. Carlier et al. ([<reflink idref="bib10" id="ref22">10</reflink>]) found an acceptable medium to very high test–retest reliability (assessments separated by one week) for the SQ-48 subscales (ICC =.79–.91), except for the aggression subscale (ICC =.65). The SQ-48 total score showed very high test–retest reliability (ICC =.93). In addition, the authors concluded that the SQ-48 is responsive to clinical change over time based on differences between pre- and post-treatment measurements (I. Carlier et al., [<reflink idref="bib8" id="ref23">8</reflink>]). Furthermore, the psychometric properties of the SQ-48 were explored within different languages (Kovács et al., [<reflink idref="bib19" id="ref24">19</reflink>]). The current study is the first to explore the psychometric properties of the Dutch SQ-48 in a sample of adults with MID-BIF.</p> <hd id="AN0186344827-5">Procedure</hd> <p>The SQ-48 was administered at intake as part of the Routine Outcome Monitoring (ROM) procedure. To investigate test–retest reliability, some participants were voluntarily tested a second time approximately three weeks later. These participants were reimbursed for their time and effort with a gift card worth ten euros. Twenty-four people participated in the test–retest after approximately three weeks, of whom fifteen (62.5%) were female. The average age of these participants was 33.5 years (<emph>SD</emph> = 11.2), and the average number of days between the first and the second administration was 22.1 days (<emph>SD</emph> = 3.4).</p> <p>Patients were excluded from the assessment when they were suffering from an acute psychosis or otherwise distorted in thinking (e.g. recent substance use and delirium) at the time of administration and were assessed when these symptoms were no longer present. An assistant was available to help patients complete the measure if they had any questions. The instructions and items were read together with the patient or verbatim to the patient. Only if necessary, alternative scripted items were used to simplify or clarify items. Also, a visual scoring card was used, which contained the answering-scale in words (<emph>never</emph> to <emph>very often</emph>), numbers (zero to four) and colors (light blue to dark blue).</p> <p>The study protocol and documents were approved by the internal research review board at both mental health services. Data on the SQ-48 and sociodemographic characteristics were extracted anonymously from the electronic patient files at one of the mental health services; therefore, informed consent was not required. Patients from the other mental health service provided written and informed consent.</p> <hd id="AN0186344827-6">Statistical Analyses</hd> <p>Internal consistency was calculated for the subscales and total scale using Cronbach's alpha and McDonald's omega. A value from.70 to.90 for Cronbach's alpha and McDonald's omega was considered to have sufficient internal consistency. A value under.70 is considered insufficient and above.90 may suggest redundancies (Tavakol & Dennick, [<reflink idref="bib23" id="ref25">23</reflink>]). To investigate the discriminant validity between the subscales, the Spearman intercorrelation (<emph>ρ</emph>) coefficients were calculated. A value of <emph>ρ</emph> <.70 was considered sufficient discriminant validity (Hodson, [<reflink idref="bib17" id="ref26">17</reflink>]). Test–retest reliability was calculated using the intraclass correlation coefficient (ICC) for the subscales and total score, using the Two Way Random model and Absolute Agreement type. The following interpretations of the ICC were used: values above.75 indicate excellent agreement,.60 to.74 indicate good agreement,.40 to.59 indicate moderate agreement, and values below.40 show poor agreement (McDowell, [<reflink idref="bib20" id="ref27">20</reflink>]). Construct validity of the SQ-48 was assessed using a confirmatory factor analysis (CFA) to evaluate to which extent the factor model of the SQ-48 fits the sample of people with MID-BIF in mental health care. A comparative fit index (CFI) greater than 0.95, a root mean square error of approximation (RMSEA), and a standardized root mean square residual (SRMR) smaller or equal to.08 indicate a good model fit (Byrne, [<reflink idref="bib7" id="ref28">7</reflink>]). Next, measurement invariance, i.e. psychometric equivalence of the instrument across groups, was assessed to determine if the gender, age, or setting (i.e. outpatient, daytreatment, inpatient, and referred to other services) were factors influencing the factor structure. To determine measurement invariance Δχ<sups>2</sups> should not be significant (Byrne, [<reflink idref="bib7" id="ref29">7</reflink>], p. 270), and the change in goodness-of-fit indices (e.g. ΔCFI and ΔRMSEA) should be smaller or equal to 0.01 (Cheung & Rensvold, [<reflink idref="bib11" id="ref30">11</reflink>]).</p> <p>All analyses were performed using IBM SPSS Statistics 29, except for the CFA, which was done by the R Package using the packages "lavaan," "lavaanPlot", and "semTools."</p> <hd id="AN0186344827-7">Results</hd> <p></p> <hd id="AN0186344827-8">Descriptive Statistics and Internal Consistency</hd> <p>Means, standard deviations, cutoff values and percentages, and internal consistency coefficients of the SQ-48 subscales are shown in Table 2. As shown, on almost all subscales more than half of the sample scored above the cutoff values. This signifies a sample with a high level of psychological distress.</p> <p>Table 2. Means, standard deviations, cutoff values and percentages, and internal consistency coefficients.</p> <p> <ephtml> <table><thead><tr><td>Scale</td><td>Mean (<italic>M</italic>)</td><td>Standard deviation (<italic>SD</italic>)</td><td>Cut-off values(I. Carlier et al., <xref ref-type="bibr" rid="bibr9">2012</xref>)</td><td>Percentage above cutoff (%)</td><td>Cronbach's alpha (<italic>α</italic>)</td><td>McDonalds omega (<italic>ω</italic>)</td></tr></thead><tbody><tr><td>Depression (MOOD)</td><td>11.79</td><td>6.55</td><td>8.0</td><td>68.54</td><td>.89</td><td>.89</td></tr><tr><td>Anxiety (ANXI)</td><td>13.39</td><td>5.88</td><td>11.2</td><td>65.73</td><td>.87</td><td>.87</td></tr><tr><td>Somatic complaints (SOMA)</td><td>8.82</td><td>6.18</td><td>8.0</td><td>49.30</td><td>.80</td><td>.80</td></tr><tr><td>Social phobia (SOPH)</td><td>8.85</td><td>5.63</td><td>9.0</td><td>45.54</td><td>.85</td><td>.86</td></tr><tr><td>Agoraphobia (AGOR)</td><td>4.06</td><td>3.98</td><td>2.0</td><td>55.40</td><td>.78</td><td>.79</td></tr><tr><td>Aggression (AGGR)</td><td>4.65</td><td>3.79</td><td>5.0</td><td>37.56</td><td>.77</td><td>.78</td></tr><tr><td>Cognitive problems (COGN)</td><td>11.22</td><td>4.78</td><td>11.0</td><td>51.64</td><td>.78</td><td>.78</td></tr><tr><td>Vitality/optimism (VITA)</td><td>12.52</td><td>5.39</td><td>15.0</td><td>65.73*</td><td>.84</td><td>.85</td></tr><tr><td>Work/study functioning (WORK)</td><td>4.34</td><td>4.96</td><td>–</td><td>–</td><td>.84</td><td>.85</td></tr><tr><td>Total (TOT)</td><td>65.93</td><td>29.17</td><td>–</td><td>–</td><td>.94</td><td>.95</td></tr></tbody></table> </ephtml> </p> <p>2 <emph>Note</emph>. *Percentage of participants under cutoff value, as a lower score on the vitality subscale indicates more psychological distress.</p> <p>The reliability coefficients ranged from.77 (subscale aggression) to.94 (total scale) for Cronbach's alpha and from.78 (subscales aggression and cognitive problems) to.95 (total scale) for McDonald's omega. All subscale reliability coefficients were acceptable (.70 ≤ <emph>α/ω</emph> <.90). The total scale showed high internal consistency (<emph>α</emph> =.94, <emph>ω</emph> =.95), which might suggest redundancies. Cronbach's alpha of the total scale did not go below.941 or exceeded.945 if any one item was removed.</p> <p>The item reliability analysis within the subscales showed that removing three items would slightly improve the internal consistency of the subscale. These items were item 10 ("I argued with others," aggression subscale), item 23 ("I could hardly express myself," social phobia subscale) and item 34 ("I looked forward to my plans and goals for the future," vitality subscale). Cronbach's alpha increased less than.01; therefore, removing these items was not required to improve the overall validity of the SQ-48. The removal of item 21 ("I had trouble with controlling my anger," aggression subscale) and item 25 ("I did not dare to go alone to a crowded shop," agoraphobia subscale) would decrease the internal consistency of the subscales notably (<emph>α</emph> decreased.12 for both items). This would suggest that these items are extremely important to measure the concept of the specific subscale.</p> <hd id="AN0186344827-9">Scale Differentiation</hd> <p>Spearman rho intercorrelations of the SQ-48 subscales are shown in Table 3. The correlations ranged from −.03 to.68. The highest correlations were observed between the depression, anxiety, social phobia, agoraphobia, and cognitive problems subscales (<emph>ρ</emph> >.60). The lowest correlations were observed in the vitality/optimism and work functioning subscales.</p> <p>Table 3. Spearman rho (ρ) correlations between subscales of the SQ-48.</p> <p> <ephtml> <table><thead><tr><td /><td>MOOD</td><td>ANXI</td><td>SOMA</td><td>SOPH</td><td>AGOR</td><td>AGGR</td><td>COGN</td><td>VITA</td></tr></thead><tbody><tr><td>ANXI</td><td>.68**</td><td /><td /><td /><td /><td /><td /><td /></tr><tr><td>SOMA</td><td>.56**</td><td>.58**</td><td /><td /><td /><td /><td /><td /></tr><tr><td>SOPH</td><td>.48**</td><td>.67**</td><td>.31**</td><td /><td /><td /><td /><td /></tr><tr><td>AGOR</td><td>.45**</td><td>.62**</td><td>.50**</td><td>.58**</td><td /><td /><td /><td /></tr><tr><td>AGGR</td><td>.37**</td><td>.40**</td><td>.27**</td><td>.18**</td><td>.21**</td><td /><td /><td /></tr><tr><td>COGN</td><td>.66**</td><td>.68**</td><td>.56**</td><td>.48**</td><td>.47**</td><td>.40**</td><td /><td /></tr><tr><td>VITA</td><td>.33**</td><td>.19**</td><td>.18*</td><td>.06</td><td>.11</td><td>.03</td><td>.20**</td><td /></tr><tr><td>WORK<sup>#</sup></td><td>.12</td><td>.16*</td><td>.03</td><td>.14</td><td>.10</td><td>.11</td><td>.17*</td><td>−.03</td></tr></tbody></table> </ephtml> </p> <p>3 *Significant at <emph>p</emph> ≤.05 level. **Significant at <emph>p</emph> ≤.01 level. <sups>#</sups>For all correlations de total sample (<emph>n</emph> = 213) was used except for the work functioning subscale (<emph>n</emph> = 147) because of missing values due to not having work or attending a social daycare.</p> <hd id="AN0186344827-10">Test–Retest Reliability</hd> <p>Table 4 shows the intraclass correlations between the consecutive administrations three weeks apart. The test–retest reliability of the social phobia, aggression, cognitive problems, vitality, and work subscales is good. The subscales of depression, anxiety, somatic complaints, and total scale show moderate agreement. Only the test–retest reliability of the agoraphobia subscale is poor.</p> <p>Table 4. Intraclass correlations of the SQ-48 (sub)scales.</p> <p> <ephtml> <table><thead><tr><td>Scale</td><td>ICC</td><td>95% CI</td></tr></thead><tbody><tr><td>Depression (MOOD)</td><td>.48**</td><td>.09–.72</td></tr><tr><td>Anxiety (ANXI)</td><td>.59**</td><td>.26–.80</td></tr><tr><td>Somatic complaints (SOMA)</td><td>.46**</td><td>.08–.72</td></tr><tr><td>Social phobia (SOPH)</td><td>.60**</td><td>.28–.81</td></tr><tr><td>Agoraphobia (AGOR)</td><td>.29</td><td>−.13–.61</td></tr><tr><td>Aggression (AGGR)</td><td>.64**</td><td>.34–.83</td></tr><tr><td>Cognitive problems (COGN)</td><td>.72**</td><td>.46–.87</td></tr><tr><td>Vitality/optimism (VITA)</td><td>.60**</td><td>.28–.81</td></tr><tr><td>Work/study functioning (WORK)<sup>#</sup></td><td>.74**</td><td>.44–.89</td></tr><tr><td>Total (TOT)</td><td>.50**</td><td>.15–.75</td></tr></tbody></table> </ephtml> </p> <p>4 **Significant at <emph>p</emph> ≤.01 level. <sups>#</sups>For all correlations the total sample (<emph>n</emph> = 24) was used except for the work functioning subscale (<emph>n</emph> = 19) because of missing values due to not having work or attending a social daycare. CI = confidence intervals.</p> <hd id="AN0186344827-11">Confirmatory Factor Analysis</hd> <p>The CFA was conducted to test the fit of the subscales of the first administration of the SQ-48. The work subscale was not included in the analysis because of the great number of missing values due to participants' not having work or not attending a social daycare. The CFI of the eight-factor model (.84) indicated an insufficient fit of the data. However, the RMSEA (.07) and SRMR (.07) indicated a good model fit. The fit of the total scale as a one-factor model was insufficient (CFI=.64, RMSEA =.11, SRMR =.09).</p> <p>To improve the model fit of the eight-factor model, correlation between the following items with modification indices above twenty was permitted: Within the depression subscale between item 13 ("I considered my death or suicide") and item 19 ("I did not want to live anymore), within the somatic complaints subscale between item 26 ("I was shaking or trembling") and item 31 ("I felt shaky or I had shivers"), and within the vitality subscale between item 29 ("I was optimistic about my future") and item 42 ("I felt energetic and high-spirited"). In addition, the correlation between item 4 from the agoraphobia subscale ("I felt anxious while I was in a crowd (of people")" and item 5 from the somatic complaints subscale ("I felt palpitations") was allowed, as heart palpitations are common in people with agoraphobic complaints (e.g. Azab, [<reflink idref="bib2" id="ref31">2</reflink>]). Allowing correlation between these items improved the model fit slightly. The results showed that the CFI (.89) improved but was still insufficient. The RMSEA (.05) and the SRMR (.07) still indicated a good model fit. Figure 1 shows the plot of the significant (<emph>p</emph> <.05) standardized factor loadings of the items on the subscales and the additional between item correlations to improve the model fit. As shown, the standardized factor loadings of the items with the subscales range between.48 and.93 were adequate in size and pointed to none of the items being redundant.</p> <p>Graph: Figure 1. Eight-factor model of the SQ-48 with standardized correlations.</p> <p>As part of the validity tests, the measurement invariance of the eight-factor structure with modifications was tested to determine if the SQ-48 measures identical construct with the same structure across different control variables: gender, age, level of intellectual disability (i.e. MID or BIF) and setting. For the measurement invariance test of the setting, two groups were included in the measurement invariance test: outpatients (<emph>n</emph> = 89) and patients receiving day treatment (<emph>n</emph> = 64). The other two groups (i.e. inpatients and referred to other services) were too small (<emph>n</emph> = 39 and 21, respectively) to be included in the measurement invariance test.</p> <p>As shown in Table 5, the CFI is lower than desired for all control variables, but RMSEA showed a good model fit for all control variables, except setting. Δχ<sups>2</sups> was not significant for age group, level of intellectual disability and setting. The differences in the goodness-of-fit indices (i.e. ΔCFI and ΔRMSEA) for all variables showed values smaller than 0.01. Results showed significant differences in factor structure between genders. This means that there are differences in factor loadings, means, and error terms on items between males and females, but the factor configuration is still similar. For the age groups, scalar invariance is achieved and the different goodness-of-fit indices indicate a good model fit. Therefore, measurement invariance can be cautiously concluded for the control variable of age. For the control variables level of intellectual disability and setting, measurement invariance is established, which means that the factor structure of the SQ-48 is robust to influence of treatment setting and the level of intellectual disability.</p> <p>Table 5. Fit indices of the measurement invariance tests.</p> <p> <ephtml> <table><thead><tr><td>a. Gender, female (<italic>n</italic> = 134, 62.9%) and male (<italic>n</italic> = 79, 37.1%)</td></tr><tr><td>Model</td><td>χ<sup>2</sup> (<italic>df</italic>)</td><td>CFI</td><td>RMSEA</td><td>Δχ<sup>2</sup> (Δ<italic>df</italic>)</td><td><italic>p</italic></td><td>ΔCFI</td><td>ΔRMSEA</td></tr></thead><tbody><tr><td>1. Configural invariance</td><td>2534.2 (1656)</td><td>.827</td><td>.071</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>2. Metric invariance</td><td>2597.8 (1691)</td><td>.821</td><td>.071</td><td>63.59 (35)</td><td>.002**</td><td>.006</td><td>.000</td></tr><tr><td>3. Scalar invariance</td><td>2657.4 (1726)</td><td>.816</td><td>.072</td><td>59.64 (35)</td><td>.006**</td><td>.005</td><td>.000</td></tr><tr><td>4. Residual invariance</td><td>2688.5 (1734)</td><td>.812</td><td>.072</td><td>31.04 (8)</td><td><.001***</td><td>.005</td><td>.001</td></tr><tr><td>Total <italic>n</italic> = 213. *<italic>p</italic> ≤.05; **<italic>p</italic> ≤.01; ***<italic>p</italic> ≤.001.</td></tr><tr><td>b. Age groups, 18-35 years (<italic>n</italic> = 110, 51.6%) and 36-72 years (<italic>n</italic> = 103, 48.4%)</td></tr><tr><td>Model</td><td>χ<sup>2</sup> (<italic>df</italic>)</td><td>CFI</td><td>RMSEA</td><td>Δχ<sup>2</sup> (Δ<italic>df</italic>)</td><td><italic>p</italic></td><td>ΔCFI</td><td>ΔRMSEA</td></tr><tr><td>1. Configural invariance</td><td>2541.6 (1656)</td><td>.830</td><td>.071</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>2. Metric invariance</td><td>2569.1 (1691)</td><td>.831</td><td>.070</td><td>27.43 (35)</td><td>.82</td><td>.001</td><td>.001</td></tr><tr><td>3. Scalar invariance</td><td>2607.1 (1726)</td><td>.831</td><td>.070</td><td>38.02 (35)</td><td>.33</td><td>.001</td><td>.001</td></tr><tr><td>4. Residual invariance</td><td>2623.9 (1734)</td><td>.829</td><td>.070</td><td>16.82 (8)</td><td>.03*</td><td>.002</td><td>.000</td></tr><tr><td>Total <italic>n</italic> = 213. *<italic>p</italic> ≤.05; **<italic>p</italic> ≤.01; ***<italic>p</italic> ≤.001.</td></tr><tr><td>c. Level of intellectual disability, MID (<italic>n</italic> = 105, 53.6%) and BIF (<italic>n =</italic> 91, 46.4%)</td></tr><tr><td>Model</td><td>χ<sup>2</sup> (<italic>df</italic>)</td><td>CFI</td><td>RMSEA</td><td>Δχ<sup>2</sup> (Δ<italic>df</italic>)</td><td><italic>p</italic></td><td>ΔCFI</td><td>ΔRMSEA</td></tr><tr><td>1. Configural invariance</td><td>2554.1 (1656)</td><td>.816</td><td>.075</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>2. Metric invariance</td><td>2603.1 (1691)</td><td>.813</td><td>.075</td><td>49.05 (35)</td><td>.06</td><td>.003</td><td>.000</td></tr><tr><td>3. Scalar invariance</td><td>2631.3 (1726)</td><td>.814</td><td>.074</td><td>28.16 (35)</td><td>.79</td><td>.001</td><td>.001</td></tr><tr><td>4. Residual invariance</td><td>2646.2 (1734)</td><td>.813</td><td>.074</td><td>14.87 (8)</td><td>.06</td><td>.001</td><td>.000</td></tr><tr><td>Total <italic>n</italic> = 196. *<italic>p</italic> ≤.05; **<italic>p</italic> ≤.01; ***<italic>p</italic> ≤.001.</td></tr><tr><td>d. Setting, outpatients (<italic>n</italic> = 89, 58.2%) and day treatment patients (<italic>n</italic> = 64, 41.8%)</td></tr><tr><td>Model</td><td>χ<sup>2</sup> (<italic>df</italic>)</td><td>CFI</td><td>RMSEA</td><td>Δχ<sup>2</sup> (Δ<italic>df</italic>)</td><td><italic>p</italic></td><td>ΔCFI</td><td>ΔRMSEA</td></tr><tr><td>1. Configural invariance</td><td>2657.5 (1656)</td><td>.735</td><td>.089</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>2. Metric invariance</td><td>2695.9 (1691)</td><td>.734</td><td>.088</td><td>38.38 (35)</td><td>.32</td><td>.001</td><td>.001</td></tr><tr><td>3. Scalar invariance</td><td>2741.5 (1726)</td><td>.731</td><td>.088</td><td>45.66 (35)</td><td>.11</td><td>.003</td><td>.000</td></tr><tr><td>4. Residual invariance</td><td>3752.1 (1734)</td><td>.731</td><td>.088</td><td>10.59 (8)</td><td>.23</td><td>.001</td><td>.000</td></tr></tbody></table> </ephtml> </p> <p>5 Total <emph>n</emph> = 153. Inpatients (<emph>n</emph> = 39) and referred to other services (<emph>n</emph> = 21) were excluded, as the groups were too small. *<emph>p</emph> ≤.05; **<emph>p</emph> ≤.01; ***<emph>p</emph> ≤.001.</p> <hd id="AN0186344827-12">Discussion</hd> <p>The objective of the present study was to explore the psychometric properties of the SQ-48 in adults with MID-BIF in a specialized mental health care setting. The results suggest that the SQ-48 has adequate consistency, structural validity, test–rest reliability, and a similar factor structure as in the general population.</p> <p>The SQ-48 in our sample of people with MID-BIF was internally consistent, which is similar to that in the original study (I. Carlier et al., [<reflink idref="bib9" id="ref32">9</reflink>]). As there were no large differences between the respective alpha and omega coefficients (largest difference.02), a differential impact of items did not seem to influence the internal consistency (Graham, [<reflink idref="bib16" id="ref33">16</reflink>]), meaning that all items were of comparable influence. This was further confirmed by the item reliability analysis. In addition, the results showed an acceptable discriminant validity. The highest correlations were observed between the depression, anxiety, social phobia, agoraphobia, and cognitive problems subscales. Many studies have found similarly strong correlations between these factors, which are denominated into a distinct internalizing spectrum (Watson et al., [<reflink idref="bib25" id="ref34">25</reflink>]). The lowest correlations were observed in the vitality/optimism and work functioning subscales, which points to these two subscales measuring independent concepts. However, some of these low correlations were non-significant and should therefore be interpreted with caution. Overall, the interscale correlations are lower than reported in the original study (I. Carlier et al., [<reflink idref="bib9" id="ref35">9</reflink>]).</p> <p>The test–retest reliability was moderate to good. The agoraphobia subscale showed poor interclass correlation, most likely due to the lack of variability in item scores (i.e., mainly low scores) combined with a relatively small sample size. Overall, the test–retest reliability mentioned in a follow-up study by I. V. E. Carlier et al. ([<reflink idref="bib10" id="ref36">10</reflink>]) was higher. This may be due to the differences in the timeframe between the two consecutive administrations (i.e. one week for the study by Carlier and colleagues and three weeks for the current study).</p> <p>Two out of three fit-indices for an eight-factor structure of the SQ-48 (subscale WORK was excluded) indicated a good model fit. These results are partially in accord with the original study by I. Carlier et al. ([<reflink idref="bib9" id="ref37">9</reflink>]). The one-factor structure for the total scale showed an insufficient model fit. These results point to an eight-dimensional construct instead of a one-dimensional construct. It is advised that the eight subscales should be used for treatment planning and evaluation instead of the total score. Because of the good internal consistency in this study, it is assumed that the verbal comprehension abilities of this sample did not influence the model fit indices. The factor structure of the SQ-48 is robust to the influence of the treatment setting, the level of intellectual disability and age.</p> <p>Some limitations of the current study need to be considered when interpreting the results. First, the test–retest sample size was small. Moreover, no detailed information about the specific treatment between the test–retest interval was available. Therefore, it is not clear whether the treatment influenced the agreement between the assessments. Thus, in the future research the test–retest sample size should be larger, the interval between assessments should be approximately one week (as in the Carlier et al. study) and more information about the treatment should be available. Second, the number of participants was not equally distributed over the different treatment settings, which limited the analyses on structural robustness. Third, gender did seem to influence the factor structure of the SQ-48. However, no previous research on the SQ-48 has researched gender as influencing factor on the reliability and validity and therefore results could not be compared. However, a study by Drapeau et al. ([<reflink idref="bib13" id="ref38">13</reflink>]) also found measurement invariance across gender on the K6 psychological distress scale. They concluded that the measurement invariance was due to higher mean levels of psychological distress in women, rather than a difference in construct validty. In the current study, the mean level of distress was also higher in women compared to men, though more research is needed to confirm the influence on the construct validity. Lastly, no data was collected on how often items were simplified or clarified. Eventhough, patients asked for little to no simplification or clarification in our experience, the influence of the level of assistance could not be researched.</p> <p>Thus, future research on the SQ-48 in people with MID-BIF should focus on responsiveness to therapeutic change, on the influence of gender on the factor structure, the influence of cultural and language aspects and on the influence of the level of assistance needed. Also, future research should include a sample with MID-BIF without comorbid psychiatric problems to determine reference values. In this way, the reliability coefficients of the MID-BIF sample can be compared to other patient groups so that the impact of the intellectual and adaptive limitations on the validity and reliability can be determined further. Together, this would provide complementary evidence for the valid and reliable use of the SQ-48 for treatment planning and evaluation in people with MID-BIF.</p> <p>In conclusion, the SQ-48 has good psychometric properties when used in people with MID-BIF in mental health care. These results are in line with the results found in the studies on the reliability and validity of the SQ-48 by I. Carlier et al. ([<reflink idref="bib9" id="ref39">9</reflink>], [<reflink idref="bib10" id="ref40">10</reflink>]). 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  Data: Psychometric Properties of the Symptom Questionnaire--48 in Adults with Mild Intellectual Disability or Borderline Intellectual Functioning in Mental Health Care
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  Data: <searchLink fieldCode="AR" term="%22Renate+A%2E+van+der+Heijden%22">Renate A. van der Heijden</searchLink><br /><searchLink fieldCode="AR" term="%22Kim+van+Zutven%22">Kim van Zutven</searchLink><br /><searchLink fieldCode="AR" term="%22Inge+P%2E+C%2E+Verhagen%22">Inge P. C. Verhagen</searchLink><br /><searchLink fieldCode="AR" term="%22Renate+Venhorst%22">Renate Venhorst</searchLink><br /><searchLink fieldCode="AR" term="%22Jeanet+G%2E+Nieuwenhuis%22">Jeanet G. Nieuwenhuis</searchLink><br /><searchLink fieldCode="AR" term="%22Hubert+P%2E+L%2E+M%2E+Korzilius%22">Hubert P. L. M. Korzilius</searchLink><br /><searchLink fieldCode="AR" term="%22Paul+T%2E+van+der+Heijden%22">Paul T. van der Heijden</searchLink><br /><searchLink fieldCode="AR" term="%22Robert+Didden%22">Robert Didden</searchLink>
– Name: TitleSource
  Label: Source
  Group: Src
  Data: <searchLink fieldCode="SO" term="%22Journal+of+Mental+Health+Research+in+Intellectual+Disabilities%22"><i>Journal of Mental Health Research in Intellectual Disabilities</i></searchLink>. 2025 18(3):265-279.
– Name: Avail
  Label: Availability
  Group: Avail
  Data: Routledge. Available from: Taylor & Francis, Ltd. 530 Walnut Street Suite 850, Philadelphia, PA 19106. Tel: 800-354-1420; Tel: 215-625-8900; Fax: 215-207-0050; Web site: http://www.tandf.co.uk/journals
– Name: PeerReviewed
  Label: Peer Reviewed
  Group: SrcInfo
  Data: Y
– Name: Pages
  Label: Page Count
  Group: Src
  Data: 15
– Name: DatePubCY
  Label: Publication Date
  Group: Date
  Data: 2025
– Name: TypeDocument
  Label: Document Type
  Group: TypDoc
  Data: Journal Articles<br />Reports - Research
– Name: Subject
  Label: Descriptors
  Group: Su
  Data: <searchLink fieldCode="DE" term="%22Psychometrics%22">Psychometrics</searchLink><br /><searchLink fieldCode="DE" term="%22Questionnaires%22">Questionnaires</searchLink><br /><searchLink fieldCode="DE" term="%22Adults%22">Adults</searchLink><br /><searchLink fieldCode="DE" term="%22Mild+Intellectual+Disability%22">Mild Intellectual Disability</searchLink><br /><searchLink fieldCode="DE" term="%22Mental+Health%22">Mental Health</searchLink><br /><searchLink fieldCode="DE" term="%22Test+Validity%22">Test Validity</searchLink><br /><searchLink fieldCode="DE" term="%22Test+Reliability%22">Test Reliability</searchLink><br /><searchLink fieldCode="DE" term="%22Foreign+Countries%22">Foreign Countries</searchLink><br /><searchLink fieldCode="DE" term="%22Symptoms+%28Individual+Disorders%29%22">Symptoms (Individual Disorders)</searchLink>
– Name: Subject
  Label: Geographic Terms
  Group: Su
  Data: <searchLink fieldCode="DE" term="%22Netherlands%22">Netherlands</searchLink>
– Name: DOI
  Label: DOI
  Group: ID
  Data: 10.1080/19315864.2024.2416697
– Name: ISSN
  Label: ISSN
  Group: ISSN
  Data: 1931-5864<br />1931-5872
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Introduction: Increasingly more self-report measures of psychological distress are used as screening tools in mental health care for treatment planning and routing outcome monitoring. Research on the psychometric properties and utility of these measures in individuals with mild intellectual disability or borderline intellectual functioning (MID-BIF) are limited, even though this target group accounts for a large proportion of individuals treated in mental health care services. The aim of the present study was to explore the psychometric properties of the SQ-48, a self-report on psychological distress, when used in adults with MID-BIF. Methods: The SQ-48 was administered to 213 patients of two specialist mental health services for MID-BIF in the Netherlands. A second administration took place after three weeks in a test-retest design (N = 24). Results: The SQ-48 has adequate internal consistency, discriminant validity, test-retest reliability, and factor structure when used in adults with MID-BIF. Conclusion: This study provides preliminary evidence that the limitations in intellectual and adaptive functioning in people with MID-BIF do not influence the reliability and validity of the SQ-48 and can be used reliably in this population.
– Name: AbstractInfo
  Label: Abstractor
  Group: Ab
  Data: As Provided
– Name: DateEntry
  Label: Entry Date
  Group: Date
  Data: 2026
– Name: AN
  Label: Accession Number
  Group: ID
  Data: EJ1502931
PLink https://search.ebscohost.com/login.aspx?direct=true&site=eds-live&db=eric&AN=EJ1502931
RecordInfo BibRecord:
  BibEntity:
    Identifiers:
      – Type: doi
        Value: 10.1080/19315864.2024.2416697
    Languages:
      – Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 15
        StartPage: 265
    Subjects:
      – SubjectFull: Psychometrics
        Type: general
      – SubjectFull: Questionnaires
        Type: general
      – SubjectFull: Adults
        Type: general
      – SubjectFull: Mild Intellectual Disability
        Type: general
      – SubjectFull: Mental Health
        Type: general
      – SubjectFull: Test Validity
        Type: general
      – SubjectFull: Test Reliability
        Type: general
      – SubjectFull: Foreign Countries
        Type: general
      – SubjectFull: Symptoms (Individual Disorders)
        Type: general
      – SubjectFull: Netherlands
        Type: general
    Titles:
      – TitleFull: Psychometric Properties of the Symptom Questionnaire--48 in Adults with Mild Intellectual Disability or Borderline Intellectual Functioning in Mental Health Care
        Type: main
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      – PersonEntity:
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            NameFull: Renate A. van der Heijden
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            NameFull: Kim van Zutven
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            NameFull: Inge P. C. Verhagen
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            NameFull: Renate Venhorst
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            NameFull: Jeanet G. Nieuwenhuis
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            NameFull: Hubert P. L. M. Korzilius
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            NameFull: Paul T. van der Heijden
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            NameFull: Robert Didden
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            – D: 01
              M: 01
              Type: published
              Y: 2025
          Identifiers:
            – Type: issn-print
              Value: 1931-5864
            – Type: issn-electronic
              Value: 1931-5872
          Numbering:
            – Type: volume
              Value: 18
            – Type: issue
              Value: 3
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            – TitleFull: Journal of Mental Health Research in Intellectual Disabilities
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