Comparison of unweighted and item response theory-based weighted sum scoring for the Nine-Questions Depression-Rating Scale in the Northern Thai Dialect

Background

The Nine-Questions Depression-Rating Scale (9Q) has been developed as an alternative assessment tool for assessing the severity of depressive symptoms in Thai adults. The traditional unweighted sum scoring approach does not account for differences in the loadings of the items on the actual severity. Therefore, we developed an Item Response Theory (IRT)-based weighted sum scoring approach to provide a scoring method that is more precise than the unweighted sum score.

Methods

Secondary data from a study on the criterion-related validity of the 9Q in the northern Thai dialect was used in this study. All participants were interviewed to obtain demographic data and screened/evaluated for major depressive disorder and the severity of the associated depressive symptoms, followed by diagnosis by a psychiatrist for major depressive disorder. IRT models were used to estimate the discrimination and threshold parameters. Differential item functioning (DIF) of responses to each item between males and females was compared using likelihood-ratio tests. The IRT-based weighed sum scores of the individual items are defined as the linear combination of individual response weighted with the discrimination and threshold parameters divided by the plausible maximum score based on the graded-response model (GRM) for the 9Q score (9Q-GRM) or the nominal-response model (NRM) for categorical combinations of the intensity and frequency of symptoms from the 9Q responses (9QSF-NRM). The performances of the two scoring procedures were compared using relative precision.

Results

Of the 1,355 participants, 1,000 and 355 participants were randomly selected for the developmental and validation group for the IRT-based weighted scoring, respectively. the gender-related DIF were presented for items 2 and 5 for the 9Q-GRM, while most items (except for items 3 and 6) for the 9QSF-NRM, which could be used to separately estimate the parameters between genders. The 9Q-GRM model accounting for DIF had a higher precision (16.7%) than the unweighted sum-score approach.

Discussion

Our findings suggest that weighted sum scoring with the IRT parameters can improve the scoring when using 9Q to measure the severity of the depressive symptoms in Thai adults. Accounting for DIF between the genders resulted in higher precision for IRT-based weighted scoring.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12874-022-01744-0.

Services for depression and suicide in Thailand

Depression, together with suicide is an important contributor to the burden of disease in Thailand. Until recently, depression has been significantly under-recognized in the country. The lack of response to this health challenge has been compounded by a low level of access to standard care, constraints on mental health personnel and inadequate dissemination of knowledge in caring for people with these disorders. In the past decade, significant work has been undertaken to establish a new evidence-based surveillance and care system for depression and suicide in Thailand that operates at all levels of health-care provision nationwide. The main components of the integrated system are: (i) community-level screening for depression in at-risk groups, using a two-question tool; (ii) assessment of the severity of depression using a nine-question scale; (iii) diagnosis and treatment by general practitioners; (iv) psychosocial care provided by psychiatric nurses; (v) continuous care for relapse and suicide prevention; and (vi) promotion of mental well-being and prevention of depression in at-risk populations. Factors such as appropriate financial mechanisms, capacity-building programmes for health-care workers, and robust treatment guidelines have contributed to the success and sustainability of this comprehensive surveillance and care system. By 2016, more than 14 million people at risk had been screened for depression and received mental health education; more than 1.7 million people with depression had received psychosocial interventions; 0.7 million diagnosed patients had received antidepressants; and 0.8 million were being followed up for relapse and suicide prevention. The application of this surveillance and care system has led to an enormous increase in the accessibility of standard care for people with depressive disorders, from 5.1% of those with depressive disorders in 2009 to 48.5% in 2016.