I'm attempting a 'difference-in-differences' analysis of a health policy intervention, over 3 years. I'd appreciate advice on my methodology.
Year 0: Health clinics are given financial incentives for offering three different treatment indicators (e.g. for diabetes, for high blood pressure, for asthma).
Year 1: Control group (asthma) continues with incentives, as in year 0. The two other indicators (the two intervention groups) stop being incentivised financially. (So I can assess the impact of dropping the financial incentives with a DiD approach, after 1 year.)
Year 2: The control group continues as before. Intervention 1 (diabetes) goes BACK to being incentivised (as in year 0). Intervention 2 (high blood pressure) continues without being incentivised financially - but clinics are told they should use 'peer review schemes' to maintain performance.
Is there an effective way to quantify the impact of:
a) intervention group 1 returning to the original payment incentive in year 2
b) intervention group 2 continuing without payment incentives in year 2 (as in year 1) - albeit with new requirement that they maintain performance with peer review.
For each year (0, 1, 2) I have data for each of the three groups (control group, intervention group 1, intervention 2) for every single clinic in the country (around 450 clinics).
My approach so far:
Do a standard DiD comparison between years 0 and 1, to assess impact of stopping financial incentives (comparing control and intervention groups)
Do an extended DiD analysis of intervention 2, to assess impact of stopping financial incentives over two years - comparing it to the control group. This approach isn't perfect because, after year 1, clinics were told explicitly to maintain intervention 2 performance with peer review (so the situation changed slightly). But I'd also like to draw conclusions about whether or not performance was maintained after the introduction of 'peer review' (presumably that can be done without a DiD analysis)
Do a DiD analysis of intervention 1, from year 1 to 2 (to assess impact of returning to financial payments, after dropping them in year 1) - use intervention 2 as the control group (which continued without incentives from years 1 to 2). Again, this isn't perfect, because of the added requirement for intervention 2 (after year 1) that clinics maintain their performance with peer review.
Is there any way this approach can be improved? Thanks.