Table 6

Extent of bias associated with misclassification* of the effectiveness algorithm according to observed response rate

Observed response rate

True response rate**

Bias (observed-true)/true (%)

30%

30%

< 1%

40%

36%

10%

50%

43%

16%

60%

49%

21%

*From Table 4, where the positive predictive value (PPV) was 76% and the negative predictive value (NPV) was 90%. **Computed as True rate = Observed rate × (PPV + NPV-1)-NPV + 1 [39]. Numbers are rounded to the nearest whole integer but the actual values were used to calculate the bias.

Curtis et al. Arthritis Research & Therapy 2011 13:R155   doi:10.1186/ar3471