Real and simulated experimental data and theoretical data from quantal response experiments were used to make a comparison between the analysis of data from a quantal response experiment and data from a direct enumeration experiment. The method of analysis for each is differentiated, thereby enhancing the utility of the quantal response experiment in sterilization studies. From this comparison it appears that the Stumbo estimate of the D value is biased. Furthermore, the Stumbo estimate depends upon the spore load per replicate in quantal response type experiments, which makes experimental comparisons difficult. Another estimate of D is demonstrated which overcomes some of these shortcomings.