Demographers study the structure, interactions, and shifting trends of human populations. To date, artificial and opt-in populations have received little attention. This work applies demographic methods to the field of philosophy to understand its past, current, and future directions. For example, consider this adapted population graph showing North American philosophy PhDs in the period 1905–2005.
Population graphs show the overall structure of a population based on age group (i.e., birth year cohort); male and female figures are often shown separately, since sex has important implications for other demographic trends involving birth rate, education, health, and so on. Population graphs often highlight the growth and age structure of the population, as well as changes in female and male birth rate and mortality.
For the purpose of studying philosophy, this standard population graph was adapted in several ways. Although individuals enter a population through birth or immigration, entry into academic disciplines is best characterized by completing a doctoral degree in the field. Thus, the year in which a person’s doctoral degree was awarded was used as a proxy for his/her birth year in the field. (In this graph, there is no correlate for exit because many actual years of death are unknown and, even if they were, it is likely the individuals exit the field through retirement or unemployment years or decades before they die.) As a result, the graph is not a true population graph because it does not show any existent population over a single period of time, but rather several continuous populations within the period indicated. Nevertheless, the chart captures overall trends of growth and decline and gives a sense of the age and gender of the current population.
 Data on doctoral degrees was compiled from dissertations housed in libraries at 17 North American institutions, as well as records contained in Dissertation Abstracts International, Thomas Bechtle’s Dissertations in Philosophy Accepted at American Universities, 1861-1975, and annual lists of doctoral degrees printed in the Review of Metaphysics. Sex was imputed to degree recipients based on first and middle names, as well as additional research about specific individuals. Of the original 14,926 degree recipients, the sex of 911 (6.1%) could not be determined, and these were excluded from the visualization