Table 6.
Example of Outcome Misclassification Yielding an Unbiased Risk Ratio
| Outcome Status (n) | ||||||
|---|---|---|---|---|---|---|
| Exposure Status | D+ | D− | Total (n) | Risk a | RR | RD |
| Correctly classified data | ||||||
| Exposed | 100 | 400 | 500 | 0.20 | 2.00 | 0.10 |
| Unexposed | 50 | 450 | 500 | 0.10 | 1.00b | 1.00b |
| Outcome misclassified with perfect specificity and imperfect 60% sensitivityc | ||||||
| Exposed | 60 | 440 | 500 | 0.12 | 2.00 | 0.06 |
| Unexposed | 30 | 470 | 500 | 0.06 | 1.00b | 1.00b |
Abbreviations: RD, risk difference; RR, risk ratio.
a Risk = number in D+/total number.
b Referent.
c 40% of individuals with the disease are misclassified as not having the disease, in both the exposed and unexposed groups. In this example, the RR for exposed versus unexposed is unchanged, but the RD is biased towards the null by 40%.