Table 1 Maximum scores and items for each section in the questionnaires assessing quality of the research in case–control and cohort studies.

Questionnaire sections	Design
	Case–control	Prospective cohort	Retrospective cohort
Definition and follow‐up of the cohort
Maximum score	NA	11	18
Items	NA	1–7	1–8
Losses to follow‐up
Maximum score	NA	13	11
Items	NA	8–12	9–12
Measurement of disease incidence
Maximum score	NA	6	5
Items	NA	13–16	13–15
Selection of the cases and controls
Maximum score	25	NA	NA
Items	1–11	NA	NA
Inclusion and exclusion criteria for cases and controls
Maximum score	9	NA	NA
Items	12–16	NA	NA
Occupational exposure measurement
Maximum score	18	9	8
Items	17–28	17–20	16–18
Control of confounding variables
Maximum score	9	9	9
Items	29, 30	21, 22	21, 22
Precision
Maximum score	2	2	2
Items	31, 32	23, 24	23, 24
Internal and external validity
Maximum score	8	8	8
Items	33, 34	25, 26	25, 26
Likelihood for biases
Maximum score	40	32	32
Items	35–39	27–30	27–30
Global Quality Index*
Maximum score	111	90	93

NA, not applicable.

*In the text the Global Quality Index (GQI) for each study is presented as a percentage of these maximum scores.