Fig. 16. The gold standard problem. Various tests have been used to diagnose luteal phase deficiency. Although the physiologic gold standard would be the luteal phase that accompanies normal conceptive cycles, this gold standard does not exist because the luteal phase is altered by human chorionic gonadotropin secretion from pregnancy. Various investigators have attempted to validate their favorite diagnostic method according to another nonstandardized diagnostic method. Other investigators have attempted to validate their diagnostic method by reporting the numbers of patients who get pregnant after luteal phase deficiency treatment as diagnoses by a particular method. This latter approach does not take into account the background (treatment-independent) pregnancy rate. BBT, basal body temperature.