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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
RE: st: Kwallis in a loop [now p-value of the Kwallis] |

Date |
Sun, 6 Nov 2005 22:39:57 -0000 |

This all looks more complicated than needed, especially given the alternative of a few seconds' copy and paste. -tabstat- is not really designed for matrix output, as is illustrated by the fact that you have to massage things with -tabstatmat-, which I rather regret writing, as it tempts people into bad habits. Similarly, -makematrix- was a kind of experiment, which was interesting at least for me, but it is disconcerting whenever people use it and there are better tools available for what they are doing. It doesn't support -by:-, partly because other things do. In your case, you intend using it to put a scalar in a 1 X 1 matrix, which is not necessary. -statsmat-, on the other hand, does seem closer to what you want to do here. The main part of that is wanting a matrix, because you want to use -mat2txt-, because you want a tab-delimited file for output. Or so I understand. Let's generalise to (1) several variables and keep (2) a single grouping variable, and write a program on the grounds that we can write something a little more widely applicable with not much more effort. This produces a matrix with Ns, means and sums of ranks and the Kruskal-Wallis P-value. I rather gave up on where the variable names should go. program pourherve version 9 syntax varlist [if] [in], by(varname) matrix(str) marksample touse markout `touse' `by', strok qui count if `touse' if r(N) == 0 error 2000 tempname col work qui tab `by' if `touse' matrix `col' = J(`r(r)',1,.) matrix colnames `col' = "P-value" qui foreach v of local varlist { tempvar rank egen `rank' = rank(`v') if `touse' statsmat `rank', by(`by') s(N sum mean) matrix(`work') mat `work' = `work' , `col' kwallis `v', by(`by') matrix `work'[1,4] = /// max(chiprob(r(df), r(chi2_adj) + 1e-20),.0001) matrix `matrix' = nullmat(`matrix') \ `work' drop `rank' } end With your data pourherve index2 prov_ass, by(sodas3cl) matrix(m) mat2txt, matrix(m) saving(table5) may help you along. Given other variables just change the varlist. Nick n.j.cox@durham.ac.uk Herve STOLOWY > Thanks again for your help. I applied your suggestion and it > works. The principle of the loop is fine. > > I have a new question concerning how to get the p-value of > the kwallis test. > > Here is my loop: > > local action replace > foreach var of varlist index2 prov_ass { > egen rank_`var' = rank(`var') if sodas3cl < . > bysort sodas3cl : egen ranksum_`var' = sum(rank_`var') > by sodas3cl : egen rankmean_`var' = mean(rank_`var') > > statsmat `var', s(N) by(sodas3cl) mat(m1) > tabstat rankmean_`var', by(sodas3cl) save > tabstatmat m2 > matrix m3 = m1,m2 > statsmat rankmean_`var', s(N 0) mat(m4) > matrix m5 = m3\m4 > makematrix m6, from(r(chi2_adj) formula to add) label : > kwallis `var', by(sodas3cl) > matrix m7 = m5\m6 > mat2txt, matrix(m7) saving(table5) `action' > local action append > } > > As the p-value of the test is not returned as a scalar, I > learnt from prior postings to the list that I should add the > relevant formula. For the Mann-Whitney U test, I know that > the formula is: 2*normprob(-abs(r(z))). > > Unfortunately, I don't know the right formula for the Kwallis > test. I searched in the kwallis ado file but don't find it. I > certainly miss it. * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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