I am trying to replicate some odds ratio calculations which are reported in this paper. For example in the paper on page 3 in the Strome et al. data for tonsil: it states there are 52 cases and 48 controls. HPV % cases = 40% and controls = 6%.
Converting the percentages to raw figures, I get the following 2×2 table:
Case Control
HPV positive 21 3
HPV negative 31 45
Therefore the odds ratio should $=\frac{21\cdot45}{31\cdot3} = 10.16$.
However the paper reports this particular odds ratio as 18.2 on the following page. Does anyone know why this is? Are they using a different formula?