Analysis

To determine the overall quality of the measurement properties of the different questionnaires we combined the different studies per PROM (for each language) by combining their results (ratings), adjusted for the methodological quality (fair, good or excellent) and the consistency of their results. The overall rating for a measurement property was recorded as “positive,” “indeterminate” or “negative.” Furthermore, we assessed a level of evidence (strong, moderate, limited, conflicting, unknown) using the COSMIN checklist in a similar manner to that proposed by the Cochrane Review Group (see Table 1) [29].

Levels of evidence for the overall quality of the measurement property

^aRating is based on Table 1 per study, where + refers to a positive result and − for a negative result

^bThe criteria of methodological quality are based on the COSMIN checklist

We made recommendations concerning the use of a certain PROM per language, based upon the best evidence synthesis. Ideally, a PROM should have strong positive evidence on all measurement properties; however, if there was moderate evidence, a recommendation was still made. In case multiple PROMs showed similar ratings in a specific language, both were presented. If there were no studies with at least fair methodology, no recommendations were made and if there was only limited evidence, caution was advised.