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Table 2 Levels of evidence for the overall quality of a measurement property

From: Measurement properties of asthma-specific quality-of-life measures: protocol for a systematic review

Level Rating Criteria
Strong +++ or --- Consistent findings in multiple studies of good methodological quality OR in one study of excellent methodological quality
Moderate ++ or -- Consistent findings in multiple studies of fair methodological quality OR in one study of good methodological quality
Limited + or - One study of fair methodological quality
Conflicting +/- Conflicting findings
Unknown ? Only studies of poor methological quality
  1. Plus sign indicates positive rating; question mark, indeterminate rating and minus sign, negative rating.