st: linear interpolation

[Scott Cunningham <scunning@gmail.com>]

I have data from the 1980, 1990 and 2000 Census, and need to linearly  
interpolate the in-between years (1981-1989, 1991-2001, 2002-2005).   
For now, I am assuming a constant rate of growth each year.  Let D80  
equal the 1980 value, D90 equal the 1990 value and r be the rate of  
growth per year.  Solving this means solving the following equation  
for r:

D1*(1+r)^10=D2

I had two questions.  How do I create a panel for 1981-1989,  
1991-1999, 2001-2005 to insert these missing values?  Assume the data  
is in this format:

YEAR	 D		STATE
1980	100			1
1980	3			2
1990	200			1
1990	4			2

I want to create YEAR values for 1981-1989, etc., and then after  
doing that, create corresponding estimates for each state.  This  
means calculating two different values for r, and then using that  
value to estimate each of the missing years.  I think I will need to  
use the -expand- command, but I wasn't sure if there was a simple way  
to do this, such as with an ado file already created for exactly this  
sort of thing.

thanks,


scott
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