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Table 4 Risk of bias in non-randomized studies

From: Efficacy, effectiveness and safety of vaccination against human papillomavirus in males: a systematic review

Study Confounding Selection bias Classification of intervention Deviation from intervention Missing data Outcome measurement Selection of reported results Overall risk of bias
Swedish et al. 2012 [25]a + ++ ++ ++ ++
Swedish and Goldstone 2014 [34]a + ++ ++ ++ ++
Kahn et al. [24]b – – ++ ++ ++ – –
  1. ++ low risk of bias, + moderate risk of bias, − serious risk of bias, – –- critical risk of bias
  2. aUnclear selection into study; differences in follow-up time between groups; loss-to-follow up
  3. bOnly unadjusted data available; unclear selection into study; loss-to-follow up; possible misclassification of intervention