MC) researchers must determine how many replications or repeated samples to draw for each condition under investigation. MC experiments performed with too few replications may produce idiosyncratic results, but too many replications may be inefficient. The purpose of this paper is to examine the number of replications needed in MC experiments designed to investigate robustness and statistical power. A precision-based method for determining an appropriate number of replications, uniquely combined here with robustness criteria, is recommended. Using analytical and meta-Monte Carlo methods, implications of this precision-based method are considered and tables for the recommended number of replications based on the method are provided. Further, recommendations are made to enhance both the accuracy and consistency of MC studies of robustness and power using an adaptive, continuous criterion comparison method of programming combined with the precision-based approach. Ultimately, we show that tables provided here can also be used when MC researchers desire an appropriate number of replications for estimating both proportion parameters (e.g., Type I error, statistical power) and nonproportion parameters (e.g., means, regression coefficients).onte Carlo (MC) methods are used in statistics for various purposes, especially when analytical solutions or closed formulas are not possible or not easy (Mooney, 1997). In robustness studies of Type I error rates, MC researchers use computer simulation to draw many repeated samples of pseudorandom data from population distributions with known parameters such that the null hypothesis is true; therefore, all rejections of the null hypothesis are Type I errors. After many repeated samples, the proportion of rejections (π) estimates the actual probability of a Type I error under the studied conditions (e.g., violations of the statistic's assumptions). Robustness is determined by how well π estimates the nominal Type I error rate, α. In MC studies of power, conditions are set such that null hypotheses are known to be false, where the proportion of the repeated samples in which the null hypothesis is correctly rejected is used to estimate statistical power. If desired, Type II error is then generally inferred as the complement to power (i.e., Type II error = 1power). In this case, robustness can then be determined by how well 1 -π estimates the nominal Type II error rate, β.MC researchers must determine how many repeated samples (also called replications, trials, or iterations) to draw for each condition under investigation. MC experiments performed with too few replications may produce inaccurate, unstable, and idiosyncratic results, but too many replications may be inefficient (Hutchinson & Bandalos, 1997). That is, more replications result in more statistical power to detect departures from theory and more precision to estimate parameters, but there are diminishing returns as the number of replications increases.The purpose of this paper is to examine the number of replications needed ...