Table 1.

Criteria used to assess content validity strength and psychometric strength

	Content validity strength	Psychometric strength
Measures	• Target patient indication • Development process – Literature reviews (concepts or instruments) – Expert input/interviews – Patient participation (concept elicitation and/or cognitive debriefing interviews)	• Internal consistency reliability [30] Cronbach’s alpha > 0.7 • Reproducibility/test–retest reliability [31, 32] ICC > 0.7 • Construct validity [33] Correlation coefficients range from ≥ 0.3 to ≥ 0.6 • Minimum clinically important difference [34] Value(s) reported for PRO instrument • Ability to detect change Demonstrated for PRO instrument
Scoring
Strong	• Developed for target indication • Development process with involvement of patients, literature reviews and clinician experts	• 4 or 5 psychometric properties meeting threshold values
Medium	• Developed for target indication • Development process lacking patient input	• 2 or 3 psychometric properties meeting threshold values
Weak	• Not developed for target indication OR • Just one type of input in the development process	• 0 or 1 psychometric properties meeting threshold values

Threshold values for psychometric strength are shown in italics

ICC intraclass correlation coefficient, PRO patient-reported outcome