General Questions on Class or Homework Materials

Hi Foram

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Page 12 is the one with

Strata  Cases  Controls  Odds Ratio
G+E+    25     2         34.7
G+E-    10     4         6.9
G-E+    84     63        3.7
G-E-    36     100       Reference

So the first Odds Ratio (34.7) is calculated from the 2x2 table

Strata  Cases  Controls  Odds Ratio
G+E+    25     2         34.7
G-E-    36     100       Reference

which you would calculate, depending on how you learned this

OR = (25 x 100) / (36 x 2) = 34.7
OR = (25 / 2) / (36 / 100) = 34.7  [Ratio of odds]

You can then solve similarly for the other 2x2 tables. The key is that each line is with respect to the reference. so the other two are first

Strata  Cases  Controls  Odds Ratio
G+E-    10     4         6.9
G-E-    36     100       Reference

OR = (10 x 100) / (4 x 36) = 6.9

Strata  Cases  Controls  Odds Ratio
G-E+    84     63        3.7
G-E-    36     100       Reference

OR = (84 x 100) / (63 x 36) = 3.7

Best,
Tom