Dear Friedrich and Nick,
Richard Williams has reported the feature of the tabstat.
>To add to the mystery:
>
>. tabstat foreign [aw=weight], stat(count)
>
>variable | N
>-------------+----------
>foreign | 74
>------------------------
>
>. tabstat foreign [aw=weight], stat(mean)
>
>variable | mean
>-------------+----------
>foreign | .2280254
>------------------------
>
>. tabstat foreign [aw=weight], stat(sum)
>
>variable | sum
>-------------+----------
>foreign | 50950
>------------------------
>
In fact,
. sum for [aw = wei]
Variable | Obs Weight Mean Std. Dev. Min
Max
-------------+--------------------------------------------------------------
---
foreign | 74 223440 .2280254 .422423 0
1
. gen sumweight = sum(weight)
. list sumweight in l
+----------+
| sumwei~t |
|----------|
74. | 223440 |
+----------+
. di 50950/223440
.22802542
This is because we assume the value 0 or 1 for each weight unit.
Toyoto
> Dear Toyoto,
>
> The auto data has 22 observations with foreign=1, not 50950. In [R]
> tabstat we read: "aweights and fweights are allowed; see [U] 14.1.6
> weight." [U] 14.1.6 states that most Stata commands rescale the
> aweights to sum to N. However, -tabstat- does not rescale the
> weights. The fact that -tabstat- treats aweights the same way as
> fweights is not clearly documented. One could also argue that this
> behavior is inconsistent.
>
> Friedrich Huebler
>
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