Generate a variable: average annual growth rate

[Josh Wang]

Dear Statalisters,
I'd like to generate a variable "γ" called the average annual growth rate according to the formula :

Where x is the revenue in year t, n is the number of years, γ is the average annual growth rate.
I hope to have the commands to generate γ.
Thank you in advance!

Best,
Josh

I attached an example of the sample.
-----------------------

* Example generated by -dataex-. To install: ssc install dataex
clear
input float(id year revenue)
1 2001 100
1 2002  20
1 2003 100
1 2004 110
1 2005 125
2 2003  60
2 2004  50
2 2005  90
3 2001 190
3 2002 180
3 2003 100
3 2004  90
end

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[George Ford]

You'll get more interesting responses I think, but this works:

xtset id year
bys id (year): g idN = _n
egen base = mean(cond(idN==1, revenue, .)), by(id)
g y = (revenue/base)^(1/(idN-1)) - 1

[Josh Wang]

You'll get more interesting responses I think, but this works:

xtset id year
bys id (year): g idN = _n
egen base = mean(cond(idN==1, revenue, .)), by(id)
g y = (revenue/base)^(1/(idN-1)) - 1

Thank you George for your suggestion. But I found the variable I get is time-variant, I think what I need should be a time-invariant variable.

Best,
Josh

[George Ford]

To give you a sense of what's going on, observe the data for this:

bys id:  g base = revenue[1]
bys id:  g last = revenue[_N]
bys id: g N = _N

So, the growth rate from firsr/last period is

 
 bys id: g growth = (revenue[_N]/revenue[1])^(1/_N)-1

But note that the number of years used to compute that will be different if the panel is not balanced.

[Josh Wang]

To give you a sense of what's going on, observe the data for this:

bys id: g base = revenue[1]
bys id: g last = revenue[_N]
bys id: g N = _N

So, the growth rate from firsr/last period is

bys id: g growth = (revenue[_N]/revenue[1])^(1/_N)-1

But note that the number of years used to compute that will be different if the panel is not balanced.

Yes I use unbalanced panel data.
Thank you!