Two strata from a case-control investigation produce these data:
Stratum 1: a1=20, b1=5, c1=10, d1=15 (n1=50)
Stratum 2: a2=15, b2=20, c2=25, d2=40 (n2=100).
Calculate the Mantel-Haenszel pooled odds ratio (OR_MH).

• A. 2.0
• B. 0.5
• C. 1.0
• D. 3.5

Answer: (A)