Paul O'Brien
>
> I have not been able to get the table layout right to do a
> test for trend
> (NPTREND) with the following data:
>
> WEIGHT EE20mcg EE30mcg
> gained 48 24
> stable 210 114
> lost 38 18
>
> What I get is this:
>
> . tabi 48 24\210 114\38 18
>
> | col
> row | 1 2 | Total
> -----------+----------------------+----------
> 1 | 48 24 | 72
> 2 | 210 114 | 324
> 3 | 38 18 | 56
> -----------+----------------------+----------
> Total | 296 156 | 452
>
> Pearson chi2(2) = 0.2483 Pr = 0.883
>
> . list
>
> row col pop
> 1. 1 1 48
> 2. 1 2 24
> 3. 2 1 210
> 4. 2 2 114
> 5. 3 1 38
> 6. 3 2 18
>
> . nptrend row, by(col)
>
> col score obs sum of ranks
> 1 1 3 10.5
> 2 2 3 10.5
>
> z = 0.00
> Prob > |z| = 1.00
>
>
>
> The correct answer is:
> One sided P = .2965
> Two sided P = .593
>
> Where am I going wrong?
The problem is that Stata does not
know that it should look at your -pop- variable.
Try
. nptrend pop, by(row)
Incidentally, a graph created with
. ordplot row [w=pop] , by(col)
supports the idea that these groups
of responses are similar.
(For -ordplot-, type -ssc desc ordplot-.)
Nick
[email protected]
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