Which of the following factors relates to the method of setting fires?

The factor that relates to the method of setting fires is the repeated use of the same firesetting method. This suggests a pattern of behavior in which an individual consistently employs a particular technique or approach to ignite a fire. Such patterns can provide critical insight into the motives behind the firesetting, the psychological profile of the firesetter, and can also help investigators anticipate and prevent future incidents.

Understanding the method used in repeated firesetting allows investigators to identify trends and potentially link separate incidents to the same perpetrator. It can inform the development of behavior profiles and risk assessments, serving as a crucial component of the investigation.

While the other choices, such as the device used in the fire or the origin of the ignite source, are undoubtedly important factors in a fire investigation, they do not specifically address the method employed to set the fire. Similarly, changes in fuel composition may influence how a fire burns but do not inherently relate to the methodology of igniting it. Therefore, focusing on the repeated use of the same methods yields a deeper understanding of the behavior associated with firesetting.