How to use the by statement in Proc Panel

[kevin_li]

Disclaimer: Undergrad student learning how to use SAS

So I'm doing proc panel using data that looks like this

Year	State	Vehicle Miles Traveled per driver	Population Density	Centerline Miles Density	Lane Miles Density
2002	Alabama	16074.68559	88.58738276	1.86462632	3.863757528
2003	Alabama	16296.9555	88.86863461	1.86462632	3.863816764

2002	Alaska	10193.7351	1.128180415	0.024740599	0.050168144
2003	Alaska	10264.0362	1.136998568	0.024936869	0.050550171

I use the following to get some coefficients

proc sort data=WithInteractionEffects;

  by state year;

  run;

proc panel data = WithInteractionEffects;

  id state year;

  model vehicle_miles_traveled_per_drive = population_density centerline_miles_density lane_miles population_centerline_density population_lane_density centerline_lane_density;

run;

I want to include

by state;

So that it will give me regression coefficients for each state rather than just the whole thing.

Currently, when I try that it gives me

ERROR: There is only one cross section or time series observation. Computations will be

       terminated

So is there a way to achieve the result that I want?