The following visualization displays the sizes (in terms of membership) of the 50+ divisions of the American Psychological Association from 1948, when the APA’s divisional structure was first established, until 2013. It was created by Shane M. Martin using D3.js and C3.js. The data were generously supplied by APA’s Divisional Services Office.
Hovering over any point on the graph will highlight the entire curve on which it lies (i.e., the membership of that one division over time). Alternatively, hovering over the name of a division in the list below the graph will highlight that division’s membership curve in the graph. Sweeping two fingers up on your touchpad will zoom in, enabling you to see complex portions of the graph in more detail. This is especially useful near the bottom of the graph, where many divisions have memberships below 1000.
The image tells us many things about APA divisional memberships over the years. I will mention only a few highlights here. First, note that not all divisions were launched at the same time. In 1948, there were only 17 divisions (note, there has never been a Division 4 or 11; Division 6 split off from 5 in 1963). The original divisions were dedicated to topics like “General,” “Teaching,” Experimental,” “Statistics,” “Personality & Social,” and “Clinical” and “Consulting.” These last two were the direct result of the merging of the APA with the American Association for Applied Psychology, just after World War II, at the urging of the U.S. government.
More than 30 additional divisions have been added over the years since 1948. The “History” Division (26), for instance, was added in 1966. “Women” (35) was added in 1974. “Independent Practice” (42), among the largest divisions today, was added in 1982. The newest division, “Trauma” (56), was added in 2005.
Generally speaking, divisional memberships rose steadily (as did membership in the wider APA) until the mid-1990s. Since that time, however, divisional memberships have tended to fall, though some individual divisions have continued to grow (e.g., “Industrial & Organizational” ). Older division members tend to maintain their core memberships until retirement, but younger members of the APA have not joined divisions as frequently as earlier generations did. As a result, not only has divisional membership fallen over the past 20 years, but it has become older as well. The reasons for this trend have been a matter of concern in APA circles for some time. My own judgment is that once APA converted their journals to digital editions, there was less incentive to join divisions than there had been in the past. Before digital editions of journals were available, the only way to read many of APA’s (and the associated Educational Publishing Foundation’s) journals was to join the relevant division and have a hardcopy mailed to you. (Most libraries subscribed only to the most popular APA journals, but not many of the more specialized ones.) Once APA started to sell digital “packages” of their journals to university libraries, though, potential readers could access the any journal’s contents without joining the associated division. This undercut a key motivation to join divisions.
The “Clinical Psychology” Division (12) has been one of the largest since the very beginning.
Both the “Personality & Social” and “Educational” Divisions (8, 15) experienced peaks in the early 1970s, but their memberships have steadily drifted downwards since then.
The “General” Division (1) leapt upward quickly in the late 1970s and through the 1980s (possibly associated with centennial of Wundt’s Leipzig laboratory in 1979), but it fell off sharply thereafter.
The “Psychotherapy” Division (29), which only began in 1968, rapidly climbed to become the second largest division in 1994, with over 7000 members, but fell off even more quickly afterwards.
The “Women” Division (35), experienced a tremendous spike in membership in 1995, suddenly making it APA’s 4th largest division with over 6000 members, but it then fell off rapidly afterwards. The reason for this spike is not entirely clear.
The “Independent Practice” Division (42) started in 1982 with a huge initial membership, ranking 4th overall. By 1992, it had become the largest division. In 1995, it attained the largest membership of any division in APA history, with more than 10,000 members. Although its membership fell off quickly during the late 1990s, it remains among APA’s the largest divisions today.
One division that has strongly resisted the general downward membership trend is “Clinical Neuropsychology” (40), which began in 1980. It became the largest division in 2009, with more than 4000 members.