Figure 2.

Risk of bias graph depicting the assessment of the methodological quality of included primary studies. Risk of study bias items assessed: ^aStudy’s target population as a close representation of the vHL national population. ^bSampling frame as a true or close representation of the target population. ^cSample selection based on a random/consecutive process. ^dLikelihood of nonresponse bias. ^eAcceptable case definition used in the study. ^fSame mode of evaluation for all subjects. ^gNumerator and denominator appropriate.