Relevance of an evidence-based ejaculation time cutoff point for neurobiological research of premature ejaculation.

The Diagnostic and Statistical Manual (DSM)-IV definition of premature ejaculation is not based on evidence-based studies. In particular, the absence of a well-defined quantitative measure of the intravaginal ejaculation latency time (IELT) makes the DSM definition inadequate. Therefore, the DSM-IV definition should be replaced by a medical definition that incorporates both quantitative as qualitative parameters of premature ejaculation. An evidence-based medical definition should include a cutoff point of the IELT at the 0.5 and 2.5 percentiles of the IELT distribution in the general male population. Such a definition has recently been proposed on the basis of a stopwatch study of the IELT in 491 men from five different countries. Similarly, a cutoff point of ejaculation frequency in laboratory rats enhances the probability to distinguish genuine rapid-ejaculator rats. Only by the strict application of these cutoff points is the probability enhanced that human and animal neurobiological research can prove whether these sexual endophenotypes differ in brain activation, have particular genetic genotypes (polymorphisms), are strictly under genetic control, or are dependent on environmental conditions and/or genotypic/environmental interactions.