Table 1 Criteria for assessing measurement properties (adapted from Schellingerhout et al. [28])

  Internal consistency

+

Cronbach alpha > =0.70 and < 0.95

-

Cronbach alpha <0.70 or > =0.95

?

Not available, or scale/subscale not established as unidimensional

  Reliability

+

Intraclass Correlation Coefficient (ICC) > = 0.70 or Pearson’s Correlation Coefficient (r) > =0.80

-

ICC <0.70 or r <0.80

  Measurement error

+

Minimal important change (MIC) > Smallest Detectable Change (SDC)

-

MIC < = SDC

?

MIC not established

  Content validity

+

Assessed in target population that items are a complete representation of concept under measurement and that all items are relevant.

-

Questionnaire is incomplete or contains irrelevant items

?

Not available, or not assessed in target population

  Structural validity

+

Factors explain 50 % of variance

-

Factors explain less than 50 % of variance

?

Explained variance not presented

  Hypothesis testing

+

Correlation with instruments measuring related constructs is higher than unrelated constructs, AND either (correlation with instrument measuring related construct > =0.50 OR at least 75 % of hypotheses conform to expectations).

-

Correlation with instruments measuring unrelated constructs higher than related constructs OR correlation with instrument measuring related construct <0.50 OR fewer than 75 % of hypotheses conform to expectations.

?

Correlations only with unrelated constructs, or hypotheses not sufficiently-well specified.

  Cross-cultural validity

+

Original factor structure confirmed OR no differential item functioning

-

Does not conform to original factor structure, or important differential item functioning observed

?

Factor analysis or differential item functioning not presented