Which Research Design should I use?

[RebornSlippy]

I've posted this in the Academic Corner also, but no replies as yet. I'm hoping some of you folk might be able to help please.

I have to carry out a research proposal. My research question will focus on the actual length of time which has passed between one event and another, involving patients in a medical setting. Being deliberatly obtuse here, sorry, but it's quite identifying.

Basically, that's all I want to do. Quantify the length of time. So quantitative descriptive. This will be done retrospectively by accessing relevant patient records which details the two occurances. Or should in any case, but therein will be an identified weakness I guess.

So... what design should I use to do this? I have looked at Retrospective Cohort Studies, but they seem to require a Control group, which I don't need (I don't think). Another option I found was Retrospective Case Control. I'm going around in circles with it really and feel a bit bamboozled!

I'd be very grateful if anyone could give me a nudge in the right direction.