Table 2 Outcomes–measurement quality criteria according to Terwee

1

*Internal consistency: Cronbach’s alpha (Cronbach (α)), Kunder-Richardson’s coefficient (KR20 et KR21), χ2

2

*Reliability, relative measures (including test-retest reliability, inter-rater reliability and intra- rater reliability): intraclass correlation coefficient (ICC), Kappa coefficient (K), the weighting scheme description—e.g., linear quadratic

3

*Measurement error, absolute measures: standard error of measurement (SEM), smallest detectable change (SDC), or limits of agreement (LoA)

4

*Content validity, including face validity: qualitative outcomes about concept elicitation, relevance and comprehensiveness by asking patients and/or professionals, and about comprehensibility and comprehensiveness of the PROMs.

5

*Construct validity:

Structural validity: results of exploratory (EFA) or confirmatory factor analysis (CFA); results of item response theory (IRT) test for determining the (uni-) dimensionality of the scale.

Hypotheses testing, design and statistical methods adequate for the hypotheses being tested

Cross-cultural validity: confirmatory factor analysis (CFA); differential item function (DIF) between language groups assessed

6

*Responsiveness (no gold standard DHL measure available): design and statistical methods adequate for the hypotheses to be tested