Estimation of the minimal clinically important difference on the Aberrant Behaviour Checklist–Irritability (ABC-I) for people with\ud intellectual disabilities who display aggressive challenging behaviour: A triangulated approach

\ud Background\ud The minimal clinically important difference (MCID) is relevant in the estimation of improvement in a patient outcome.\ud \ud Aim\ud To determine the MCID on the Aberrant Behaviour Checklist–Irritability (ABC-I), widely used to measure the effects of intervention for aggressive challenging behaviour in people with intellectual disabilities.\ud \ud Method and procedures\ud We utilised distribution and anchor based methods to estimate the ABC-I MCID. We extracted data from 15 randomised controlled trials (RCTs) for meta-analysis. We conducted three online workshops with family carers and professionals to consider meaningful change in case vignettes of increasing severity of aggressive challenging behaviour.\ud \ud Outcomes and results\ud We did not find overlap in the range of values between the two approaches. The meta-analysis indicated a range of MCID on the ABC-I (0.05, 4.94) whilst the anchor-based estimation indicated a larger change (6.6, 16.6).\ud \ud Conclusions and implications\ud The MCID is essential in interpreting the results from intervention studies. The present work was undertaken as part of a wider programme on the development and testing of a psychosocial intervention for aggressive challenging behaviour, and it is of interest to researchers in justifying how they choose and determine the MCID on the outcome of interest.