I have blood sugar values for diabetic patients over the past few years from a clinical practice. Half way through the observation period, a treatment intervention was applied to all of the patients. My data consists of multiple blood sugar readings per person, both before and after the intervention.
I would like to compare the change in blood sugar values for each patient before and after the intervention, in order to determine if the intervention had a significant effect on blood sugar in each patient.
Which test(s) would be appropriate to achieve this? Should I be looking at the overall change in absolute blood sugar over time? Or should I be using categories (normoglycemic, prediabetic, hyperglycemic) to determine this?
I am rather new to statistics, and any help is greatly appreciated.