Minimally important differences for the EORTC QLQ-C30 in prostate cancer clinical trials

BMC Cancer

Table 3 Summary of anchor-based and distribution-based MIDs

	Anchor-based				Distribution-based*
	MID for within-group change		MID for between-group difference in change
Scale	Improvement	Deterioration	Improvement	Deterioration	0.3 SD	0.5 SD	1 SEM
PPhysical Functioning	No MID	−11	No MID	−7	4.8	7.9	4.8
Role FunctioningRF	4	−13	5	−10	5.6	9.3	7.9
Social FunctioningF	4	−5	3	−4	4.7	7.8	5.7
Fatigue	No MID	−9	No MID	−7	5.6	9.3	7.6
Pain	No MID	−6	No MID	−5	5.4	8.9	6.7
Global Quality of Life	No MID	−7	No MID	−6	5.5	9.2	7.8
Diarrhoea	14	−9	13	−9	4.5	7.5	8

The within-group MIDs are derived from the mean change method and the between-group MIDs from the linear regression
‘no MID’ is used where no MID estimate is available either due to the absence of a suitable anchor or effect size < 0.2
* The distribution-based estimated were computed at the time point for the start of treatment;
The symptom scores were reversed to follow the functioning scales’ interpretation; i.e. 0 represents the worst possible score and 100 the best possible score
Abbreviations: ES, effect size; CTCAE, common terminology criteria for adverse events; SD = standard deviation; SEM = standard error of measurement

ISSN: 1471-2407