Ulrich Kohler <[email protected]> asks,
> Does anybody know why -tabulate, summarize- displays a nonzero
> standard-deviation for a variable that is a constant?
>
> . tab seopsu if seopsu==948, sum(firstweight)
>
> Cps Pr |
> Sampl Un | Summary of firstweight
> 5:71-73 | Mean Std. Dev. Freq.
> ------------+------------------------------------
> 948 | 13949.146 .00024815 3
> ------------+------------------------------------
> Total | 13949.146 .00024815 3
>
> . sum firstweight if seopsu==948
>
> Variable | Obs Mean Std. Dev. Min Max
> -------------+--------------------------------------------------------
> firstweight | 3 13949.15 0 13949.15 13949.15
-tabulate, summarize- uses the less accurate one-pass algorithm
to compute the standard deviation while -summarize- uses the
two-pass algorithm.
We will change the algorithm in -tabulate, summarize- to use the
two-pass algorithm in a future executable update.
As a temporary workaround,
. table dummy, contents(mean firstweight sd firstweight freq)
produces a more accurate tabulation. -table- uses the two-pass
algorithm to compute the standard deviation. Even so, the
default display format is different between -summarize- and
-table-. Displaying a zero standard deviation requires using
option -format()- to change the default format in -table-.
-- Vince
[email protected]
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