Measuring the longitudinal course of voice hearing under psychological interventions: A systematic review

Trials of psychological interventions targeting distressing voices have used a range of variables to measure outcomes. This has complicated attempts to compare outcomes across trials and to evaluate the effectiveness of these interventions. Therefore, this review aimed to identify the variables that have been used to measure the longitudinal course and impact of voice hearing under these interventions and to evaluate how these variables change over time. Inclusion and exclusion criteria were applied, resulting in a total of 66 articles. Of these, 60 studies (28 RCTs, 23 uncontrolled, 9 non-randomised) were published in peer-reviewed journals, whilst 6 were recently completed or currently ongoing. The findings of this review suggest that a range of variables that are not directly relevant to psychological interventions have been used (e.g., depression, characteristics of voice hearing experience), whilst those directly impacted by psychological interventions (e.g., voice-related distress), broader concepts of outcome (e.g., functioning) and specific associated processes (e.g., self-schema) have received less attention. Findings also showed that the majority of variables demonstrated improvements, but effect sizes varied considerably across trials. This may be attributed to methodological differences such as statistical power, blinding, control groups and different methods of measurement. Our review highlights the importance of determining a set of outcomes that are directly targeted and should change under psychological interventions. Recommendations include the use of voice-related distress as a primary outcome. This can ultimately facilitate comparisons across studies and inform the development of psychological interventions.