Distribution-based estimates of minimal important difference for hospital anxiety and depression scale and impact of event scale-revised in survivors of acute respiratory failure

Objective This study will estimate distribution-based minimal important difference (MID) for the Hospital Anxiety and Depression Scale anxiety (HADS-A) and depression (HADS-D) subscales, and the Impact of Event Scale-Revised (IES-R) in survivors of acute respiratory failure (ARF). Methods Secondary analyses of data from two US and three UK studies of ARF survivors (total N=1223). HADS-D and HADS-A were used to assess depression and anxiety symptoms. IES-R assessed post-traumatic stress disorder symptoms. Standard error of measurement, minimal detectable change₉₀, 0.5 standard deviation (S.D.), and 0.2 S.D. were used to estimate MID for the combined sample, by studies, 6- and 12-month follow-ups, country and mental health condition. Results Overall, MID estimates converged to 2.0–2.5 for the HADS-A, 1.9–2.3 for the HADS-D and 0.17–0.18 for the IES-R. MID estimates were comparable across studies, follow-up, country and mental health condition. Conclusion Among ARF survivors, 2.0–2.5 is a reasonable range for the MID for both HADS subscales, and 0.2 is reasonable for IES-R. Until anchor-based MIDs for these instruments are available, these distribution-based estimates can help researchers plan future studies and interpret the clinical importance of findings in ARF patient populations.