I'm currently work on a systematic review and meta analysis. I find these measure of incidence in published studies: events (person-years at risk x 100), rate per 100 person-years, episode/person-years and episode/100 person-years. I tried to learn the concept about it but still cannot understand clearly.

Could you explain to me, give link of references, or examples about it?

How to convert them into a common metric?

Thank you for your responses.