Re: st: pweight for households

[Daniel Feenberg <feenberg@nber.org>]

On Fri, 13 May 2011, Constance Kelly wrote:

> I'm using the Current Population Survey (March Supplement) for a project, and 
> I need to derive an estimate of the number of households in the population. 
> There is a household population weight built into the data.  The problem is 
> that the data is structured by person, with individual household identifier 
> numbers, i.e.:
>
> Person I.D.	|	Household I.D.
> 1			|		1
> 2			|		1
> 3			|		1
> 4			|		2
> 5			|		3
> 6			|		3
> etc.
>
> I know that if I reshape the data from long to wide, I can get the population 
> household estimate, but I'm trying to figure out if there is a simper way to 
> derive this value.
> Any insight would be appreciated.

Althought Stata experts will believe this is a trivial problem, I want to 
show that a beginner might take a while to find the solution. You
need to know that hhdrel==1 for the household head, so all you need
to do is get the sum of the weights of those records.

First, she might try

  count if hhdrel==1 [pweight=weight]

but -count- doesn't take weights. Then try:

  summarize if hhdrel==1 [pweight=weight]

won't work because summarize doesn't take pweights

  summarize if hhdrel==1 [aweight=weight]

won't work because -summarize- doesn't offer a weighted count. Everything
else is weighted, but not the count.

  summarize weight if hhdrel==1

is closer - you get the number of records and and the mean weight so 
you could multiply the two together to find your answer.

That isn't desirable. What about -tabulate-?

  tabulate hhdrel [pw=w] if hhdrel==1

won't work because tabulate doesn't take pweights.

  tabulate hhdrel [aw=w] if hhdrel==1

gives the wrong answer.

  tabulate hhdrel [iw=w] if hhdrel==1

gives the right answer, but the definition of iweights isn't documented. 
Better to use:

  table hhdrel [pw=w] if hhdrel==1

which is documented or even

  egen sum=sum(weight) if hhdrel==1
  summarize sum

or -table-, -collapse-, and possibly 7 other ways, but the lack
of pweights on many of the commands is a mystery to me - I never have
any other kind.

Daniel Feenberg




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