Regulators often specify default values that are considered acceptable for use in risk analyses as input to regulatory decisions. Because both performing and validating a detailed risk analysis of a complex system are costly and time-consuming undertakings, the use of default values can greatly facilitate the process of performing a risk analysis in the first place as well as the process of reviewing and verifying the risk analysis. It may also ensure more uniform in quality of risk analyses. However, different regulatory agencies differ in their approaches to the use of default values, and the implications of these differences are not yet widely understood. Moreover, large heterogeneity among licensees makes it difficult to set suitable defaults. This paper focuses on the effect of default values on estimates of risk. Some insights on the effects of different levels of conservatism in setting defaults will be provided. The results can help decision makers evaluate the levels of safety likely to result from their regulatory policies.