Table 2.

Demonstration of Simpson's paradox in the pooling of data from three observational studies, showing the value of meta-analysis

	Mortality
	Treatment	Placebo	Risk ratioa	Significance
Study 1	97/492 = 19.7%	202/802 = 24.8%	0.794	0.03
Study 2	590/795 = 74.2%	410/510 = 80.4%	0.924	0.01
Study 3	300/610 = 49.2%	286/490 = 58.4%	0.843	0.002
Pooled data	987/1,897 = 52.0%	898/1,812 = 49.6%	1.050	0.13

Meta-analysis of the above data (using [40]), fixed-effects model: Q statistic = 3.398, P = 0.18; combined risk ratio = 0.898, P = 0.0001.

^aTreatment/placebo.