Judith Abrams
>
> I believe there is an error in kwallis2. I wrote to the
> author and he
> disagreed. The reason for my concern is the null case.
> According to my
> understanding, if there are only 2 groups, kwallis and
> kwallis2 should
> produce the same pvalues, but they do not. For example,
> using the auto data
>
> kwallis trunk, by(foreign)
>
> Test: Equality of populations (Kruskal-Wallis test)
>
> +---------------------------+
> | foreign | Obs | Rank Sum |
> |----------+-----+----------|
> | Domestic | 52 | 2218.00 |
> | Foreign | 22 | 557.00 |
> +---------------------------+
>
> chi-squared = 10.045 with 1 d.f.
> probability = 0.0015
>
> chi-squared with ties = 10.134 with 1 d.f.
> probability = 0.0015
>
> **
> kwallis2 trunk, by(foreign)
>
> One-way analysis of variance by ranks (Kruskal-Wallis Test)
>
> foreign Obs RankSum RankMean
> --------------------------------
> 0 52 2218.00 42.65
> 1 22 557.00 25.32
>
> Chi-squared (uncorrected for ties) = 10.045 with 1
> d.f. (p = 0.00153)
> Chi-squared (corrected for ties) = 10.134 with 1
> d.f. (p = 0.00146)
>
> Multiple comparisons between groups
> -----------------------------------
> (Adjusted p-value for significance is 0.025000)
>
> Ho: trunk(foreign==1) = trunk(foreign==2)
> RankMeans difference = 17.34 Critical value = 10.72
> Prob = 0.000764 (S)
Sorry, but what's the difference here, apart
from display format?
Nick
[email protected]
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