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

Hassiotis et al. (2022) asked a simple question: how big must a drop on the ABC-I be before families notice real change?

They blended three ways to find the answer. First, they pooled past drug trials. Next, they ran two workshops with carers and clinicians. Last, they checked what statisticians call a minimal detectable change.

The number crunching said any drop between 0.05 and 4.94 points matters.

The people who live and work with clients said the drop must be 6.6 to 16.6 points.

The two views never met in the middle.

Ahlborn et al. (2008) already warned that rating scales alone can hide real change. They told teams to pair scales with direct observation. The new gap Angela found backs up that warning.

Robinson et al. (2011) showed that when drugs and behaviour plans run together, old-style drug RCTs often miss small but vital gains. Their fix—single-case designs—fits the wide MCID range Angela reports.

Dai et al. (2023) found CBT helps mild-ID clients only on small, low-quality studies. Because many used the ABC-I, Angela’s wide band helps explain why some trials looked “good” and others “flat.”

Poppes et al. (2010) noted staff often rate severe behaviour as “minor.” Their survey hints at why carers in Angela’s workshop set the MCID bar higher than the maths did.

Next time you read “no significant change on the ABC-I,” ask which MCID the authors picked. If they used the low maths anchor, a 5-point drop may still feel huge to the family. Share both numbers in reports. Tell teams and funders why a carer-noticed change can outrank a p-value.