Groups	Number of simulations	A priori power	Sample size
Number of metastases in MMTV-PyMT; Postn+/+ mice and MMTV-PyMT; Postn−/− mice	10,000*	81.2%	12 per group

^*The original data were randomly sampled from, with replacement, to create simulated data sets. For a given n (the number of observations) 10,000 simulations were run and the Chi-square goodness of fit test and regression coefficient (Genotype (Postn^−/−)) was calculated for each simulated data set. Any model fit with p < 0.05 was excluded. The power was then calculated by counting the number of times p ≤ 0.05 and dividing by the number of model fits.