Table 2.

Estimations of risk ratios based on data in table 1

Estimation 1	[(500+900+1000)/(25000+15000+10000)]/[(250+450+500)/(25000+15000+10000)]=2
Estimation 2	[(760+900+400)/(38000+15000+4000)]/[(120+450+800)/(12000+15000+16000)]=1.13
Test 1	[(60+225+600)/(6000+7500+12000)]/[(60+225+200)/(6000+7500+4000)]=1.25
Estimation 3	(760/38000)/(120/12000)=2; (900/15000)/(450/15000)=2; (400/4000)/(800/16000)=2; Weighted estimate = 2
Test 2	(60/6000)/(60/6000)=1; (225/7500)/(225/7500)=1; (600/12000)/(200/4000)=1.
Estimation 4	(760/38000)/(120/12000)=2; (1300/19000)/(1250/31000)=1.69; Weighted estimate= 1.74.
Test 3	(60/6000)/(60/6000)=1; (825/19500)/(425/11500)=1.14.