When you model the between estimator of you panel data, you regress the averages of the explanatory variables of the subjects against the averages of the outcome variables of the subjects.
But in this regression model, do you have to include an intercept?
Out of our textbook:
The between estimator exploits the cross-sectional dimension (differences between units) of the data by regressing the individual averages of y on the individual averages of x and a constant using OLS
I have played around with the example data of the book of Gujarati: Basic in econometrics, chapter 16. You can find the data here: http://shazam.econ.ubc.ca/student/gujarati/table15.4
This is the plot I made (the colors represent 3 different companies):
On the plot you can see the Pooled OLS regression data and the fixed effects (aka within estimator) regression data. How would the between estimator look like? Does it have one intercept or three? And what if all the data points of the companies lie exactly above each other, so they have the same average x?