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From |
"Paul O'Brien" <paul.obrien@afe2.org.uk> |

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

Subject |
Re: st: RE: NPTREND problem |

Date |
Mon, 11 Nov 2002 20:14:44 +0000 |

Thanks Nick, The treatments are ethinly estradiol (EE) 20mcg v EE 30 mcg and response is weight change, so I think your first response was right. Is that so? Paul On 11/11/02 5:15 pm, "Nick Cox" <n.j.cox@durham.ac.uk> wrote: > I replied to 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-.) >> > > No, I think my advice here on -nptrend- > is wrong: I followed your previous > path too readily. In fact, it > is not at all clear that this > is a problem for -nptrend- at > all. Your response appears > to be (ordered) categorical > and your covariate something > on two levels. > > I think the graph still makes sense > and it suggest that there is no > relationship worth talking about. > > Nick > n.j.cox@durham.ac.uk > * > * 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/ * * 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/

**Follow-Ups**:**RE: st: RE: NPTREND problem***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

**References**:**st: RE: NPTREND problem***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

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