Hi there,
In today's climate, it is fairly difficult to go from non-designated preliminary to categorical. From year to year, most programs are not losing categorical residents. Your best shot is at a program that has research years. These programs are able to adjust the number of reasearch years up or down to accomodate the proper number of residents. For example, if a categorical resident elects to take another year of research (good project with lots of publication potential), then another resident may come out of the research lab early to take that slot or a non-designated prelim may slide into it.
Apply to categorical residency slots if you KNOW that you want to do surgery. The percentages are not with you if you are applying to a preliminary slot hoping to go categorical. This happens but it is happening less frequently as most categorical surgery slots are filling in the MATCH and there were no huge number of PGY-2 slots open as fewer people who did match categorical are leaving their programs.
If you choose your categorical programs very carefully and interview wisely (provided you are realistic about your grades and board scores), you can probably match into a categorical slot.
njbmd 🙂