<p>My guess is that it’s mostly prelim programs filled via match. I just learned that there is a difference between a transitional year an a prelim year: <a href=“http://www.doctorsintraining.com/blog/figuring-out-the-transitional-preliminary-and-categorical-year-for-residency-application/[/url]”>http://www.doctorsintraining.com/blog/figuring-out-the-transitional-preliminary-and-categorical-year-for-residency-application/</a></p>
<p>They might still be mostly filled during match but the article’s point is that a one year thing is more likely to be open than a categorical spot. Also a categorical spot will lock you in to a potentially different speciality while a one year thing leaves more options open immediately (but of course requires applying again)</p>