Table 3 Quality assessment based on evaluation of bias
Author, year | Selection bias | Exposure bias | Outcome assessment bias | Confounding factor bias | Analytical bias | Attrition bias | Overall likelihood of bias based mainly on selection and confounding |
|---|---|---|---|---|---|---|---|
O’Leary et al. 2009 [30] | Minimal (sample selected from a general population rather than a select group) | Low (indirect assessment (postal survey, mailed question)) | Minimal (direct question to mother) | Minimal (assessed for common confounders) | Minimal (analyses appropriate for type of sample (if matched)) | Moderate (11 to 20% attrition but reasons for loss to follow-up not explained) | Minimal |
Faden and Graubard 2000 [29] | Minimal (sample selected from general population, Eligibility Criteria explained) | Low (indirect assessment (postal survey, mailed question)) | Minimal (direct question to mother) | High (not assessed for confounders) | Low (analyses not accounting for common statistical adjustment and sample size calculation not performed but all eligible patients studied) | Moderate (11 to 20% but reasons for loss to follow-up not explained) | High |
Greene et al. 1990 [31] | Moderate (sample selection ambiguous but may be representative) | Minimal (direct questioning (interview) or completion of survey by mother at the time of exposure or close to time of exposure) | Minimal (direct question to mother) | Minimal (assessed for common confounders) | Low (analyses not accounting for common statistical adjustment, power calculation performed) | High (>20% attrition but reasons for loss to follow-up not explained) | Moderate |