Unfortunately, even though considerable data are available for both radiologists and RTs performing mammography, all the data needed for comprehensive projection models are not available. Estimates of the age distributions of practitioners are available, but because formal certification is not a requirement for the practice of mammography in all states, complete data on all new entrants to mammography practice are not available. In addition, reliable data on departures from practice are vague at best. However, it is clear from the basic age distribution data that the proportion of RTs performing mammography past the age of 65 is much lower than comparable proportions for most health professions.
Both the radiologist and technologist projections provided in this study are based on an age-cohort flow model. Typical calculations are described in the diagram in Figure C-1, which represents a segment from the complete model shown in Tables 4–4 and 4–5 in Chapter 4 of this report.
Because there are no special certificates that all radiologists performing mammography must earn in order to read mammograms, there is no independent data source that identifies or counts new entrants into mammography practice. Nor is there an independent source of data about the numbers of practitioners who leave mammography practice, whether by death, retirement, or other departure. These data shortcomings preclude the development of a full-blown age-cohort flow model. It is necessary to make a number of assumptions to fill in the missing data.
The status quo estimates of new RTs performing mammography are based on data from ASRT on the number of people completing the mammography certification exam in recent years. Data from ASRT show that approximately 1,150 people take this exam. We have assumed that all of those who take the exam will practice mammography. Although some of those taking the exam may not enter practice, others not taking the exam will enter practice in some states and settings.