Re: st: how to create an average of previous observations

[Daniel Simon <dhs29@cornell.edu>]

A revision to my question: I can now see that creating X_AVG is not 
difficult, except for the case of multiple observations with the same date. 
However, I still need help to create X_AVG without using values of X that 
share the same date. Thanks. Daniel

At 02:40 PM 10/18/2006 -0400, you wrote:

> Hi  - I have data on a variable, X, for a set of individuals. Each 
> observation also has the date that X was recorded. I want to create a new 
> variable, X_AVG, which is the mean value of X for all observations with a 
> date that precedes the date for the current observation. X_AVG would be a 
> moving average, that would incorporate all observations with earlier dates.
>
> Example:
>
> Obs     Date            X       X_AVG
> 1       1/1/2004        4       .
> 2       1/2/2004        3       4
> 3       1/4/2004        5       3.5
> 4       1/5/2004        2       4
> 5       1/8/2004        8       3.5
> 6       1/10/2004       5       4.4
> 7       1/10/2004       8       4.4
> 8       1/11/2004       3       5
>
> I want to know how to create X_AVG. And, in particular, is there a way to 
> deal with cases like observation 7, which has the same date as observation 
> 6. In that case, I would not want to use the value of X in observation 6 
> to create X_AVG for observation 7.
>
> I hope that this is clear enough. Thanks. Daniel
>
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