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Our Methods

Criteria for considering articles and Minimal Important Differences for PROMID


Primary studies determining an MID using longitudinal or cross-sectional anchor-based methodology for one or more PROMs


PROMs of interest measure health-related quality of life, functional ability, symptom severity and psychological distress or well-being

Minimal important differences

Any anchor-based MID irrespective of participants’ condition or disease, type of intervention used in the study, nature of the anchor or methodology


Teams of two reviewers screen titles and abstracts independently and in duplicate for potentially eligible studies. Any studies identified as potentially relevant by either screener are selected for full text review, again performed in duplicate. Disagreements between reviewers are resolved by discussion or, if needed, by consultation with a third adjudicator.


For each MID, we abstract information pertaining to:

  • Country of the study
  • Population demographics
  • PROM characteristics
  • Interventions administered in the context of the MID estimation
  • Anchor details (i.e. type, construct(s), range of options/categories/values, threshold selected to represent a “small but important difference”, specific anchor-based method)
  • MID estimate, its associated measure of variability and direction
  • Details regarding MID determination (e.g. number of patients informing the MID estimate, duration of follow up (if applicable), analytical (or estimation) approach, correlations between the PROM and anchor)

credibility assessment

We define credibility as “the extent to which the design and conduct of studies measuring MIDs are likely to have protected against misleading estimates”.

All MIDs indexed in our inventory have an associated credibility rating made using an instrument developed by our group. Details regarding the development of the instrument, its characteristics and reliability can be found here (hyperlink development and reliability study reference).

The instrument is designed for assessment of an individual MID estimate; thus, each MID estimate from a single study providing multiple estimates warrants its own credibility evaluation. The tool includes two components: 1) a core instrument with five criteria applicable to any anchor-based MID estimation, and 2) an extension of the core instrument with four criteria addressing global ratings of change – also referred to as a transition rating – anchors.

With the exception of the first item, which has a yes/no response, each item in the instrument provides a five-point adjectival scale. The range of response options for remaining items include:

  • Definitely yes (we have no issue regarding credibility, and we are very confident that the true MID lies close to the estimated MID)
  • To a great extent
  • Not so much
  • Definitely no (there is a substantial issue regarding credibility, and we have very little confidence in the MID estimate)
  • Impossible to tell

Two reviewers independently conduct the credibility evaluation, resolving disagreements by discussion with input and the presence of a third reviewer for quality control.