Effect of an emergency contraceptive pill intervention on pregnancy risk behavior--an erroneous conclusion.

The study by Raymond and Weaver is a good example of how data from a good study can be used for another purpose leading to erroneous conclusions. The authors performed a secondary analysis of the data from a randomized controlled trial (RCT) to determine if increased access to emergency contraceptive pills (ECPs) leads to risky (unprotected) sex. The original RCT published in 2006 was designed to assess whether a cause-and-effect relationship exists between increased access to ECP and ECP use/risky (unprotected) sex/pregnancy. In the original well-conducted RCT 1490 women were randomly assigned to either a treatment group with increased access to ECP (unlimited supply of free ECP) or a control group-obtaining ECP through usual-care at clinics. The authors found that women with increased access to ECP were indeed significantly more likely to use ECP than women assigned to usual care but they found no differences in risky sex or pregnancy rates and concluded that increased access to ECP had an effect on ECP use but not risky sex or pregnancy. In the secondary analysis the authors examine risky sex in 148 women (74 from the treatment group and 74 from the control group) from the original RCT who had a pregnancy. While there were no differences in fully partly or entirely unprotected coital acts in the cycles ending in pregnancy they did find that there were more cycles in which there was more than one entirely unprotected coital act in the cycle ending in pregnancy in the treatment group compared to the control group (25 vs. 12 p=.017). In the 18 women with pregnancies in which ECP was used in the cycle ending in pregnancy (16 from the treatment group and 2 from the control group) they also found that pregnancies in women in the treatment group were significantly more likely to be either possibly or probably a result of ECP failure (based on cycle day of ECP administration relative to ovulation) compared to pregnancies in the women from the control group (12 vs. 1 p=.012). The authors then inappropriately assume a cause-and-effect relationship between these two outcomes - unprotected sex and ECP failures (more unprotected sex caused more ECP failures). The original RCT was designed to test a cause and- effect relationship between increased access to ECP (the intervention) and risky sex (an outcome). The authors then make a leap from here and conclude that increased access to ECP caused an increase in unprotected sex; this is in complete contrast to the original RCT conclusion. The new conclusion reached by the authors is erroneous because they failed to take into account the behaviors of women who did not become pregnant. In order to correctly conclude that women in the increased access group had more unprotected sex compared to women who did not have increased access to ECP the authors need to compare unprotected sex between treatment and control women regardless of whether or not they became pregnant. This is in fact what was done in the original RCT. It really does not make sense to take data from a gold standard study an RCT and use it in a methodologically flawed way to assess the effect of increased access to ECP; this study should be viewed with extreme caution. (full text)