Hi,

I am exploring a dataset of patient data from 20 hospitals for 3 years. Among which 9 hospitals are in the treatment group, and 11 hospitals are in the control group.

The dataset is pooled cross-sectional at the patient level, but panel at the hospital level. I have two goals:

1. Find out if a hospital-level intervention has an impact on patients' medical costs. I want to fit a fixed-effect model, controlling for hospital and year fixed effects.

First, following https://www.statalist.org/forums/for...in-differences I tried:

Code:
reg cost intervention i.hospital_id i.year_id
But the treatment effect is not significant, even I include more patient-level control variables.

Second, I tried:
Code:
xtset year_id
xtreg cost intervention i.hospital_id, fe
The treatment effect is still not significant. Am I doing it right? Are these methods correct for my goal #1?

2. Find out if a hospital-level intervention has an impact on the hospitals' admission rates.

In this case, should I aggregate the patient data to the hospital level? How could I do it? Should I take the averages of patient data in a specific year and a specific hospital?

I only have 20 observations at the hospital level, is this too small? Which method could I use if I cannot acquire more observations? Which if I can increase the sample size?


Thank you very much for your reply and favor.