I performed multiple pooled cross-sectional regressions with the same time-intervals (5years) in different years. I'm wondering now on how to aggregate the different regression outputs. Does it make sense to average the estimated coefficients or do you rather use one simple pooled regression over all $t$s? And assuming taking averages makes sense, how can you get a valid $t$-statistics?
Here is an extract of the code I used; thank you for your help.
> head(Grunfeld)
firm year inv value capital
1 1 1935 317.6 3078.5 2.8
2 1 1936 391.8 4661.7 52.6
3 1 1937 410.6 5387.1 156.9
4 1 1938 257.7 2792.2 209.2
5 1 1939 330.8 4313.2 203.4
6 1 1940 461.2 4643.9 207.2
library(plm)
data("Grunfeld", package="plm")
# Store each subset regression in myregression
myregression <- list()
# Regression on six-year subsets of Grunfeld
for(t in 1940:1950) {
myregression[[t-1939]] <- lm(inv ~ value + capital,
subset(Grunfeld, year<=t & year>=t-5))
# Rename list elements by year range of subset
names(myregression)[[t-1939]] = paste0("Years",t)
}