The debate on possible differences in thrombogenic potential between so-called "third-generation" oral contraceptives and "second-generation" pills has generated more heat than light, providing many examples of unwarranted conclusions based on inconclusive data; for example:
The numbers in question were based on 6 cases and 3 controls, and since no significant difference was found, it seems illogical to refute a possible cause for a difference in the same study. Here is another example: "The odds ratios for all third-generation monophasic contraceptives were higher [than for second-generation pills]."2 The odds ratio for the overall difference was 1.5 (95% confidence interval, 0.7-3.2), and so cannot accurately be described as being statistically higher than parity. A third example comes from another highly regarded journal, in an editorial stating that the data presented in the accompanying research letter clearly show a higher risk of fatal pulmonary embolism in women using third-generation oral contraceptives compared with those using second-generation pills containing levonorgestrel.3P values or confidence intervals for this difference are not provided in the research letter, but we calculated the odds ratio as 2.1 (95% confidence interval, 0.46-9.84), hence, not statistically significant.4