Minimal important difference to infer changes in health-related quality of life-a systematic review

The objective of the study was to assess the usability of minimal important difference (MID) and minimal clinically important difference (MCID) for measuring meaningful changes in disease-specific and generic health-related quality-of-life (HRQoL) outcomes in patient-centered care.

We adopted a two-step literature review process. First, we used PubMed and Google scholar to identify a broad range of search terms. Next, we searched OVID Medline, JSTOR, and PubMed for terms "MID," and "MCID." We excluded non-English language studies, articles older than 1995, those not related to generic- and disease-specific HRQoL measures, and protocols of future studies. Studies were grouped according to generic- and disease-specific measures. We assessed MID or MCID calculation methods, effect sizes, estimated values, and significance.

Eighty articles satisfied the inclusion criteria. Our synthesis provides a comprehensive assessment of MID or MCID for 10 generic-specific and 80 disease-specific instruments. We observed a lack of consistency in the application of methods for computing MID or MCID for generic and disease-specific HRQoL measures. Only 43 (54%) studies used both anchor and distribution methods to elicit MID or MCID. Thirty-four articles estimated MID values only, whereas 47 articles estimated MCID.

The anchor-based method yields conservative estimates of MID or MCID, compared to the distribution-based method. The distribution method does not take into account patient perspectives and should be accompanied by anchor method while computing MID. The MID should be interpreted with caution, and available estimates for a particular instrument must be used. This will help in integrating the MID estimates into the overall research or clinical plan for a specific context.