How should I punctuate this sentence:
I have found throughout my third year that the population that appeals to me is the pediatric population which is why I chose to do my research project in pediatric orthopaedics.

Using your words:

I have found throughout my third year that the population that appeals to me is the pediatric population, which is why I chose to do my research project in pediatric orthopaedics.

- Comma before which (The clause "which is why I chose to do my research project in pediatric orthopaedics" is a non-restrictive clause. Therefore, a comma is appropriate.)

Here is a lesson from the GM site on using commas and which, that and who.

I mist say that I find the sentence a little wordy.

Once suggestion might be:


My choice to research pediatric orthopaedics was influenced by the third year, which triggered my appeal for the pediatric population.

Do you mean paediatric?