Indeed, clomiphene is a racemic mixture with rather important intrinsic oestrogenic activity, due in particular to its zu-isomer. In contrast, tamoxifen does not display any demonstrable oestrogenic effects when used in the recommended dosage. In reality, the average probability of pregnancy in the tamoxifen studies is doubled. In these studies the upper limit of RR is 5.11, meaning that the possible therapeutic effect of tamoxifen may be somewhere between nil and a five fold increase. The favorable effect of tamoxifen in idiopathic oligozoospermia is sustained by the significant increase of sperm concentration observed in 23 studies, including 3 placebo-controlled studies of sperm characteristics only.
Statisticians warn for two types of errors.
A type I error occurs when a significant difference is found that is not really present, and type II error when a difference is not detected although it exists in reality. Type II errors may occur in studies including relatively small numbers of cases, and if the expected effect is moderate. When trying to assess the effect of treatment of the male partner on couple fertility, the female partners must be rigorously normal . It is well known that approximately half of the female partners of subfertile men are not optimally fertile. Moreover, these couples must accept the risk of receiving placebo and give informed consent.