The effectiveness of the Creighton Model System has been extensively studied and a meta-analysis of the system incorporating the data from five separate studies into a composite which includes 1,876 couples over 17,130 couple months of use has been published. These studies all utilizing life-table analysis and an objective assessment of pregnancies, reported the range of the method-effectiveness to avoid pregnancy at the 12th ordinal month to be 98.7 to 99.8 (with the five-study composite 99.5). The use-effectiveness to avoid pregnancy for the same time period ranged from 94.6 to 97.9 and was shown to continually improve over the 14 years of the studies (the five-study composite was 96.8) (Table 15-28).
