2007 German Study of STM Effectiveness
A well-done German study of the effectiveness of the sympto-thermal rules associated with NFP was published in 2007. The study used rules that were only slightly different from those taught by CCL, but were close enough to provide a valid comparison to the CCL method.
This study, published in the journal Human Reproduction, found a method effectiveness of 99.6% and a user effectiveness of 98.2%.
P. Frank-Hermann, J.Heil, C. Gnoth, et al. “The effectiveness of a fertility awareness based method to avoid pregnancy
in relation to a couple’s sexual behaviour during the fertile time: a prospective longitudinal study,”Human Reproduction, 2007, 1-10