| Consideration of potential confounders, measures to prevent bias, and appropriate statistical analysis were mostly lacking. |
| Variations in techniques and expertise among studies may be important confounders. |
| Important confounders can produce strong associations if not controlled for. |
| P values are from logistic regression, adjusting for confounders and taking account of dependence between related individuals. |
| We investigated these and other measures of body habitus as potential confounders. |
| Some reported both unadjusted analyses and analyses adjusted for covariates, which appropriately informs readers of the role confounders had. |
