Linear Regression and group by in R

Question

I want to do a linear regression in R using the lm() function. My data is an annual time series with one field for year (22 years) and another for state (50 sta

Answer 1

In my opinion is a mixed linear model a better approach for this kind of data. The code below given in the fixed effect the overall trend. The random effects indicate how the trend for each individual state differ from the global trend. The correlation structure takes the temporal autocorrelation into account. Have a look at Pinheiro & Bates (Mixed Effects Models in S and S-Plus).

library(nlme)
lme(response ~ year, random = ~year|state, correlation = corAR1(~year))