Several frontier AI companies test their AI systems for dual-use biological capabilities that might be misused by threat actors. But what do these test results imply about the overall risk of bioterrorist attacks? There is much expert debate about how seriously to view such threats, especially from lone wolf actors. This report creates a framework for how to convert capability evaluations into risk assessments, using a simple model that draws on historical case studies, expert elicitation, and reference class forecasting.