Risk of bias assessment instrument for systematic reviews informing WHO Global Air Quality Guidelines

Air pollution represents the single largest environmental threat to health globally. WHO is developing new Global Air Quality Guidelines, based on the most recent scientific evidence, synthetized in accordance to predefined systematic review methods. This publication includes a description of the instrument devised to assess the risk of bias in the individual studies included in the systematic reviews of adverse health effects informing the Guidelines. Further, general instructions and specific subject matter advice to guide the assessments are provided.