Hello guys,

I have the following problem and I would appreciate any help:

So Im analyzing the relationship between the quality of care (dependent variable) and the price of care (treatment / independent variable) using stata. Both variables are on firm level. Moreover, I add regional data on county level such as income, number of physicians etc (300 counties in total) and state fixed effects (10 states in total).
To account for endogeneity, I perform a IV-estimation (using ivreg2) where I instrument the price.
The data is a cross sectional data, so every observation appears once (in total 8000 observations).

My question would be if I do need to cluster standard errors on county level or if robust standard errors are sufficient. Because it severly effects the f-statistic of the excluded instruments if I use clustered standard errors on county level (its then below the magical number of 10).
Since its a cross section and the dependent and treatment variable are on firm level, I would assume using robust standard errors should be the right thing?
I would appreciate any help!

Thanks in advance.