Table 3 Second example of confounding
Unadventurous | Risk takers | Overall | |||||||||
5000 | 5000 | 10000 | |||||||||
No A users | 40% use A | (Sum over unadventurous and risk takers) | |||||||||
↙ | ↘ | ↙ | ↘ | ↙ | ↘ | ||||||
A | Not A | A | Not A | A | Not A | ||||||
0 | 5000 | 2000 | 3000 | 2200 | 8000 | ||||||
No B users | No B users | 50% use B | 30% use B | (sum) | (sum) | ||||||
↙ | ↘ | ↙ | ↘ | ↙ | ↘ | ↙ | ↘ | ↙ | ↘ | ↙ | ↘ |
B | Not B | B | Not B | B | Not B | B | Not B | B | Not B | B | Not B |
0 | 0 | 0 | 5000 | 1000 | 1000 | 900 | 2100 | 1000 | 1000 | 900 | 7100 |
OR (within risk takers) = (1000/1000)/(900/2100) = 2.33 | OR (overall, unadjusted) = (1000/1000)/(900/7100) = 7.89 | ||||||||||