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# st: Calculate variances of subsamples

 From Lars Knuth To statalist Subject st: Calculate variances of subsamples Date Wed, 2 Jun 2010 20:21:49 +0200

```Dear listers,

I have to say thanks to Martin, the recommendation of rolling was
great. Unfortunately, I have now a few problems with the
implementation.
1. -rolling- works with the "clear" option, but without it does not
("rolling r(Var), window(60) clear: summarize exret" works)
2. I need the data to calculate and store the variances for more than
1000 stock price returns in the end, so can I somehow keep all the
data and then perform -rolling- in a loop?
3. Is there also an opportunity to perform the return calculation in a loop?

I am attaching parts of the code I have so far. Any ideas would be of
great help to me.

clear*
use "C:\...\3105.dta", clear

gen int time=_n
* Return calculation
gen double exret=ex[_n]/ex[_n-1]-1 if _n>1
gen double msciret=msci[_n]/msci[_n-1]-1 if _n>1
gen double msftret=msft[_n]/msft[_n-1]-1 if _n>1
gen double appret=app[_n]/app[_n-1]-1 if _n>1
gen double geret=ge[_n]/ge[_n-1]-1 if _n>1
gen double pgret=pg[_n]/pg[_n-1]-1 if _n>1
gen double jnjret=jnj[_n]/jnj[_n-1]-1 if _n>1
gen double bpret=bp[_n]/bp[_n-1]-1 if _n>1

tsset time

* Rolling
rolling r(Var), window(60): summarize exret
rolling r(Var), window(60): summarize msciret
rolling r(Var), window(60): summarize msftret
*
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```