# RE: st: weighted cumulative sum

 From "Nick Cox" To Subject RE: st: weighted cumulative sum Date Wed, 1 Mar 2006 13:05:00 -0000

```Also see

-tssmooth-

-egen, filter()- from -egenmore- on SSC.

Nick
n.j.cox@durham.ac.uk

Austin Nichols

> bys id (year): gen exper1=pr[_n-3]/3+pr[_n-2]/2+pr[_n-1]
>
> and you could extend this to more periods (say n>3),
> but you will have exper1 missing for the first n periods
> within each panel defined by id.
>

Arik <ericl@rocketmail.com> wrote:

> > I have a panel data of firms and the number of units
> > of products they sell each year. I am trying to
> > generate some measures of production experience.
> >
> > One measure I have simply produces a cumulative sum of
> > the number of products sold up to the previous year:
> > by id: gen experience1=sum(products[_n-1])
> >
> > I am now trying to produce more sophisticated measures
> > that will discount the experience by some given rate
> > (by, say, dividing the experience by its age). The
> > idea is that last year's experience is more valuable
> > than the experience of the year before it and so on.
> >
> > For example, if I have the following dataset
> >
> > year 1 - 30 products
> > year 2 - 20 products
> > year 3 - 10 products
> > year 4 - 10 products
> > year 5 - 20 products
> >
> > Right now, my experience measure for year 4 is
> > 30+20+10=60. I am looking for a command that will give
> > me the following value: (30/3)+(20/2)+(10/1)=30

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