The differing growth patterns in the substantially overlapping applicant pools for each MD and DO schools can suggest some differences in the demographics and possibly some indications of where they are headed in the future.
While the number of first year allopathic seats has grown from both new schools opening and the increased enrollment at existing schools, applicant pool has grown at about the same rate. What has changed is that for the past decade or so, overall GPA of applicants has increased by 0.5 points and MCAT score by 2 points. Thus MD schools have become more selective in acceptance.
There has been a tremendous growth in the number of new DO schools, new branch campuses of existing schools, and increase in seats at existing schools at a much higher rate than MD. Yet the applicant pool for DO has grown at even a higher rate . This may be due to the selective pressure at MD schools, forcing applicants who a decade ago would have been very competitive do instead opt for DO. Thus on an applicant to seat basis, DO schools have become more competitive than MD schools. Additionally this competition has increased the GPA and MCAT scores of applicants at DO significantly over the past decade.
While both MD and DO seats have increased, the number of residency slots has barely budged. With a recent small increase in slots of 1,300, the number of first year allopathic residency slots will be about 27,500 in a year or two. Last year there were 22,000 first year MD students and 6,000 first year DO students, half of which typically go to allopathic residency (even though the residency programs of MD and DO are combining, it will not increase or likely change the end result of this numbers). Accounting for some attrition, you are looking at 24,000-25,000 US MD/DO graduates virtually all of which will get a residency slot, via MATCH or SOAP. That leaves 3500 at most for IMG/FMG. A decade ago it was more like 6,000-7,000 slots for IMG/FMG. Simply by numbers it becomes increasingly harder for an IMG/FMG to match.
Just to put this all in perspective, once you do complete residency, become board certified, etc, most perceived difference between MD, DO, IMG/FMG in actual clinical practice disappear. When docs talk to one another about where they trained, they mean residency