Table 2 Maximum scores for dimensions and items in the questionnaires assessing the likelihood for biases in case–control and cohort studies.

Questionnaire dimensions*	Design
	Case–control	Prospective cohort	Retrospective cohort
Selection bias
Maximum score†	44	40	43
Items‡	1–12, 15, 16, 33–35	1,2, 4–6, 8–13, 25–27	1,2,4, 6–12, 25–27
Disease misclassification bias
Maximum score	23	24	31
Items	12–16, 33, 34, 36	7, 13–16, 25, 26, 28	5–7, 13–15, 25, 26, 28
Exposure misclassification bias
Maximum score	29	25	32
Items	17–24, 33, 34, 37	17–20, 25, 26, 29	6, 7, 16–18, 25, 26, 29
Bias arising from use of surrogate informants
Maximum score	21	NA	NA
Items	25–28, 33, 34, 38	NA	NA
Bias arising from confounding
Maximum score	25	25	33
Items	29, 30, 33, 34, 39	21, 22, 25, 26, 30	6, 7, 21, 22, 25, 26, 30

NA, not applicable

*Categories of biases assessed through the different items in the questionnaires.

†Maximum score obtained from the sum of scores for items included in each dimension.

‡Items of the questionnaire (Appendices I and II, available at http://ard.bmjjournals.com/supplemental) included in each dimension.