Language-related differential item functioning between English and German PROMIS Depression items is negligible.

To investigate differential item functioning (DIF) of PROMIS Depression items between US and German samples we compared data from the US PROMIS calibration sample (n = 780), a German general population survey (n = 2,500) and a German clinical sample (n = 621). DIF was assessed in an ordinal logistic regression framework, with 0.02 as criterion for R2 -change and 0.096 for Raju's non-compensatory DIF. Item parameters were initially fixed to the PROMIS Depression metric; we used plausible values to account for uncertainty in depression estimates. Only four items showed DIF. Accounting for DIF led to negligible effects for the full item bank as well as a post hoc simulated computer-adaptive test (< 0.1 point on the PROMIS metric [mean = 50, standard deviation =10]), while the effect on the short forms was small (< 1 point). The mean depression severity (43.6) in the German general population sample was considerably lower compared to the US reference value of 50. Overall, we found little evidence for language DIF between US and German samples, which could be addressed by either replacing the DIF items by items not showing DIF or by scoring the short form in German samples with the corrected item parameters reported.

Using Patient Health Questionnaire-9 item parameters of a common metric resulted in similar depression scores compared to independent item response theory model reestimation.

OBJECTIVES: To investigate the validity of a common depression metric in independent samples. STUDY DESIGN AND SETTING: We applied a common metrics approach based on item-response theory for measuring depression to four German-speaking samples that completed the Patient Health Questionnaire (PHQ-9). We compared the PHQ item parameters reported for this common metric to reestimated item parameters that derived from fitting a generalized partial credit model solely to the PHQ-9 items. We calibrated the new model on the same scale as the common metric using two approaches (estimation with shifted prior and Stocking-Lord linking). By fitting a mixed-effects model and using Bland-Altman plots, we investigated the agreement between latent depression scores resulting from the different estimation models. RESULTS: We found different item parameters across samples and estimation methods. Although differences in latent depression scores between different estimation methods were statistically significant, these were clinically irrelevant. CONCLUSION: Our findings provide evidence that it is possible to estimate latent depression scores by using the item parameters from a common metric instead of reestimating and linking a model. The use of common metric parameters is simple, for example, using a Web application (http://www.common-metrics.org) and offers a long-term perspective to improve the comparability of patient-reported outcome measures.

[Review Model for the Assessment of Psychometric Instruments--Recommendations of the German College of Psychosomatic Medicine (DKPM)]. / Kriterienkatalog zur Beurteilung psychodiagnostischer Selbstbeurteilungsinstrumente--Empfehlung des Deutschen Kollegiums für Psychosomatische Medizin (DKPM).

OBJECTIVES: Psychometric instruments are commonly applied in psychotherapeutic research and care for the baseline assessment of symptoms, the planning of therapeutic interventions, the assessment of the longitudinal course of symptoms and outcomes of therapeutic interventions as well as quality management of care. Psychometric properties as well as economic aspects should be considered in the selection of specific instruments. It is assumed that users of psychometric instruments face a great variety of instruments and related information. For that reason, it seems challenging to absorb the current knowledge and to integrate it into clinical practice and research. Thus, it is likely that well-known, established and easily accessible instruments are commonly used, while new developed instruments might not be disseminated in research and healthcare. METHODS: Based on available international review models, the working group "Psychometrics and Psychodiagnostics" of the German College of Psychosomatic Medicine (DKPM) has developed and tested a review model specifically tailored for psychotherapeutic research and care. RESULTS: The different steps of development, as well as the final review model based on the consensus of the working group are presented. The review model contains 6 generic terms (reliability, validity, objectivity, reference groups and aspects of application) with 21 different criteria to be assessed with 0-3 asterisks (*). The criteria are clearly operationalized and the practical use of the review model is explained and discussed. CONCLUSIONS: With the review model for the assessment of psychometric instruments a well-defined evaluation system is made available for research and clinical practice which has been developed by an expert group. The review model facilitates systematic, transparent and comparative evaluation of psychometric instruments along clearly defined criteria. It also supports the selection of psychometric instruments in research and care. Next, the working group aims at disseminating and implementing the review model as well as the application and publication of reviews for different psychometric instruments based on the review model.

Assessing somatic symptom burden: a psychometric comparison of the patient health questionnaire-15 (PHQ-15) and the somatic symptom scale-8 (SSS-8).

OBJECTIVE: The Patient Health Questionnaire-15 (PHQ-15) is a frequently used questionnaire to assess somatic symptom burden. Recently, the Somatic Symptom Scale-8 (SSS-8) has been published as a short version of the PHQ-15. This study examines whether the instruments' psychometric properties and estimates of symptom burden are comparable. METHODS: Psychosomatic outpatients (N=131) completed the PHQ-15, the SSS-8 and other questionnaires (PHQ-9, GAD-7, WI-7, SF-12). Item characteristics and measures of reliability, validity, and symptom severity were determined and compared. RESULTS: The reliabilities of the PHQ-15 and SSS-8 were α=0.80 and α=0.76, respectively and both scales were highly correlated (r=0.83). The item characteristics were comparable. Both instruments showed the same pattern of correlations with measures of depression, anxiety, health anxiety and health-related quality of life (r=0.32 to 0.61). On both scales a 1-point increase was associated with a 3% increase in health care use. The percentile distributions of the PHQ-15 and the SSS-8 were similar. Using the same thresholds for somatic symptom severity (5, 10, and 15 points), both instruments identified nearly identical subgroups of patients with respect to health related quality of life. CONCLUSION: The PHQ-15 and the SSS-8 showed similar reliability and validity but the comparability of severity classifications needs further evaluation in other populations. Until then we recommend the use of the previously established thresholds. Overall, the SSS-8 performed well as a short version of the PHQ-15 which makes it preferable for assessment in time restricted settings.

Health-related quality of life, depression, and anxiety in patients with autoimmune hepatitis.

BACKGROUND & AIMS: Improving health related quality of life (HrQoL) in patients with chronic diseases such as autoimmune hepatitis (AIH) should be a major treatment goal. However, little is known on the HrQoL in patients with AIH, and the topic is not given attention in current practice guidelines. We therefore conducted a single center study evaluating HrQoL in 103 consecutive outpatients with AIH. METHODS: Patient-reported HrQoL data were analysed in relation to clinical disease parameters and compared to representative data of the German population as well as control patients. RESULTS: Based on patient-reported data, a major depressive syndrome (10.8%) was found to be five times more frequent in AIH patients compared to the general population (p<0.001). The rate of severe symptoms of anxiety was also found to be significantly increased compared to the general population (p=0.006). In seven of the eleven patients who scored for a major depressive syndrome a psychiatric comorbidity had not been diagnosed before. Major factors associated with depression and anxiety were concerns with regard to the progression of the liver disease. CONCLUSIONS: This study identified--for the first time--a high rate of previously unrecognized severe symptoms of depression and anxiety in patients with AIH. Of importance for daily clinical practice, the factors associated with these symptoms may in part be amenable to targeted counselling and adequate treatment of the disease, thereby offering the chance to improve the care and HrQoL of AIH-patients.

Standardization of depression measurement: a common metric was developed for 11 self-report depression measures.

OBJECTIVES: To provide a standardized metric for the assessment of depression severity to enable comparability among results of established depression measures. STUDY DESIGN AND SETTING: A common metric for 11 depression questionnaires was developed applying item response theory (IRT) methods. Data of 33,844 adults were used for secondary analysis including routine assessments of 23,817 in- and outpatients with mental and/or medical conditions (46% with depressive disorders) and a general population sample of 10,027 randomly selected participants from three representative German household surveys. RESULTS: A standardized metric for depression severity was defined by 143 items, and scores were normed to a general population mean of 50 (standard deviation = 10) for easy interpretability. It covers the entire range of depression severity assessed by established instruments. The metric allows comparisons among included measures. Large differences were found in their measurement precision and range, providing a rationale for instrument selection. Published scale-specific threshold scores of depression severity showed remarkable consistencies across different questionnaires. CONCLUSION: An IRT-based instrument-independent metric for depression severity enables direct comparisons among established measures. The "common ruler" simplifies the interpretation of depression assessment by identifying key thresholds for clinical and epidemiologic decision making and facilitates integrative psychometric research across studies, including meta-analysis.

[Computer adaptive tests in medicine]. / Computer Adaptive Tests in der Medizin.

Measurement of Patient-reported Outcomes (PRO) still lacks behind clinical standards. Most established tools are also either too burdensome or too imprecise to be used in clinical practice. Item Response Theory (IRT) methods and Computer Adaptive Tests (CAT) promise to overcome these shortcomings. Simulation studies have shown that individually tailored CATs can provide more precise and less burdensome measurements over a larger measurement range than static tools. Several studies with real CAT application have supported the psychometric superiority of CATs, but results from longitudinal studies are still scarce. IRT item banks also allow scoring different established tools measuring the same construct on one common metric, which could greatly facilitate the harmonization of PRO-assessments.

Impact of cross-calibration methods on the interpretation of a treatment comparison study using 2 depression scales.

BACKGROUND: Many questionnaires assessing depressive symptoms are available. Most of these questionnaires are constructed based on classical test theory, making comparisons of individual scores difficult. Item response theory (IRT) allows the comparison of scores from different instruments. In this study, the impact of IRT-based cross-calibration methods on the results of a treatment outcome study was evaluated using 2 instruments. METHODS: Data collected during admission and discharge procedures from 1066 inpatients in 2 psychosomatic clinics using different depression measures were analyzed. To achieve comparability across the applied depression measures, we used an IRT-based conversion table to transform scores from one instrument's scale to the other. Latent trait values were also estimated using different instruments in each clinic. We compared these methods to the traditional approach of using the same instrument in both clinics and examined their effects on the statistical analyses. RESULTS: There was no substantial change in the interpretation of the study results when different instruments were used. However, F values, P values, and effect sizes in the analysis of variance changed significantly. This might be attributed to differences in the content or measurement properties of the instruments. Interestingly, no difference was observed between use of transformed sum scores and latent trait values. CONCLUSIONS: IRT cross-calibration methods are a convenient way to enhance the comparability of questionnaire data in applied clinical settings but seem not to be able to overcome differences in measurement properties of the instruments. As these differences can lead to biased results, there is a need for further research into more advanced techniques.

A 4-item measure of depression and anxiety: validation and standardization of the Patient Health Questionnaire-4 (PHQ-4) in the general population.

BACKGROUND: The 4-item Patient Health Questionnaire-4 (PHQ-4) is an ultra-brief self-report questionnaire that consists of a 2-item depression scale (PHQ-2) and a 2-item anxiety scale (GAD-2). Given that PHQ-4, PHQ-2, and GAD-2 have not been validated in the general population, this study aimed to investigate their reliability and validity in a large general population sample and to generate normative data. METHODS: A nationally representative face-to-face household survey was conducted in Germany in 2006. The survey questionnaire consisted of the PHQ-4, other self-report instruments, and demographic characteristics. RESULTS: Of the 5030 participants (response rate=72.9%), 53.6% were female and mean (SD) age was 48.4 (18.0) years. The sociodemographic characteristics of the study sample closely match those of the total populations in Germany as well as those in the United States. Confirmatory factor analyses showed very good fit indices for a two-factor solution (RMSEA .027; 90% CI .023-.032). All models tested were structurally invariant between different age and gender groups. Construct validity of the PHQ-4, PHQ-2, and GAD-2 was supported by intercorrelations with other self-report scales and with demographic risk factors for depression and anxiety. PHQ-2 and GAD-2 scores of 3 corresponded to percentile ranks of 93.4% and 95.2%, respectively, whereas PHQ-2 and GAD-2 scores of 5 corresponded to percentile ranks of 99.0% and 99.2%, respectively. LIMITATION: A criterion standard diagnostic interview for depression and anxiety was not included. CONCLUSIONS: Results from this study support the reliability and validity of the PHQ-4, PHQ-2, and GAD-2 as ultra-brief measures of depression and anxiety in the general population. The normative data provided in this study can be used to compare a subject's scale score with those determined from a general population reference group.