This study aims to describe and to compare the reliability and accuracy of different methods of measuring psychiatric symptom changes in the context of substance use.
A group of 60 patients in routine methadone treatment were followed‐up during a “watchful wait” period of four to six weeks. Diagnoses of common mental disorders meeting International Classification of Diseases (ICD‐10) criteria were established using the CIS‐R structured diagnostic interview. Brief questionnaires for depression (PHQ‐9) and anxiety (GAD‐7) were used to measure symptom changes between test and retest. It was hypothesised that the accuracy of symptom changes measured using brief questionnaires may be compromised by methodological artefacts such as poor specificity, regression to the mean and measurement error. These assumptions were tested empirically.
It was demonstrated that measuring change using conventional cut‐offs in brief symptom questionnaires tends to overestimate the prevalence of common mental disorders and the rates of improvement. Using higher cut‐off scores calibrated in samples of alcohol and drug users, in combination with a reliable change index results in more conservative and reliable estimates of symptom change.
This paper presents a considered discussion on the relative merits and limitations of alternative psychiatric symptom measurement methods. These methodological recommendations may be of interest to research and clinical practice concerned with evaluating changes in comorbid depression and anxiety. Important questions are also raised about the modest degree of symptom changes typically observed during a watchful wait period.
