Definition of the categories used for classifying cross sectional studies
| Category | Definition (according to the criteria listed in table 1) |
| 4 | Criteria (a–e) are all met. |
| 3 | Criteria (a, b, andd) are met; criteria (c or e, or both) are only partly met |
| 2 | (a) Exposure assessment at least qualitatively—for example, job name only |
| (b) Criterion (b) is met | |
| (d) Only one or two of the four most important confounding factors considered | |
| (c and e) These criteria may or may not be met | |
| 1 | Still less comprehensive than category 2 |