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Reconstructing the 2 × 2 table.
| b | c | |
|---|---|---|
| Risk difference |  |
 |
| Risk ratio |  |
 |
| Odds ratio* |  |
 |
| Odds ratio† |  |
 |
Determine the values of b and c first. Second, for all effect measures, 
and a = n -(d + b + c).
s0 or s is estimate of standard error calculated from the p-value.
*Estimate 
and both proportions known.
†Estimate , one proportion 
, and p-value known.
