Table 6 

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

Observed response rate 
True response rate** 
Bias (observedtrue)/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 + NPV1)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 