Epidemiologic studies use information from several sources, including questionnaires and data from cell phone service providers, to estimate radiofrequency radiation exposure in groups of people. Direct measurements are not yet possible outside of a laboratory setting. Estimates from studies reported to date take into account the following:
How regularly study participants use cell phones (the number of calls per week or month)
The age and the year when study participants first used a cell phone and the age and the year of last use (allows calculation of the duration of use and time since the start of use)
The average number of cell phone calls per day, week, or month (frequency)
The average length of a typical cell phone call
The total hours of lifetime use, calculated from the length of typical call times, the frequency of use, and the duration of use