 It is likely that both of these caveats play some role in explaining an apparent discrepancy between the Bendor/Swistak results and the Nowak/Sigmund simulations. One would expect Bendor/Swistak's minimal stabilizing frequency to provide some indication of the length of time that a population plays a particular strategy. A strategy requiring a large invasion to overturn is likely to prevail longer than a strategy requiring only a small invasion. A straightforward calculation reveals that \(\bP_1\) has a relatively low minimum stabilizing frequency. It is overturned by invasions of unconditional defectors exceeding \(10\%\) of the population. Yet in the Nowak/Sigmund simulations, \(\bP_1\)-like strategies predominate over TFT-like strategies. Since the simulations required imperfection and since they generated a sequence of mutants vastly larger than the original population, there is no real contradiction here. Nevertheless the discrepancy suggests that we do not yet have a theoretical understanding of EPDs sufficient to predict the strategies that will emerge under various plausible conditions.