Probability is expressed as a percentage value, with 100 percent (1.0) as the highest probability of occurrence and 0 percent (0.0) as lowest. Given that this is a qualitative estimate of occurrence, it is still important to attempt to develop a reasonable level of confidence in the results by gathering as much data as possible. Because threat is tied to the time horizon of your planning and preparedness activities, identification of the relationship of the threat to that time is important.