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From |
Christian Bustamante <cdeb77@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: R:R:st Mata question |

Date |
Sun, 5 Jul 2009 18:52:38 -0500 |

Hi Carlo, Thanks for your help, but I apparently it doesn't works for what I need because I have vector with means a sds, not "observarions", thing that is not trivial. I've continued my tryings whit this: forvalues i=1/52 { scalar m1=dy04[1,`i'] scalar s1=S04[1,`i'] scalar m2=dy07[1,`i'] scalar s2=S07[1,`i'] ttesti N04 m1 s2 N07 m2 s2 mat tvalues[1,`i']=r(t) mat pvalues[1,`i']=r(p) } But stata propmt says: "'N04' found where integer expected" and "'m1' found where number expected", so i ask: there is a way to convert an scalar in a "integer" or in a "number"? Bests regards On Sun, Jul 5, 2009 at 5:26 AM, Carlo Lazzaro<carlo.lazzaro@tiscalinet.it> wrote: > Dear Christian, > the following is a a fine-tuning of my yesterday's temptative answer to your > query, again not in Mata language. > Let's assume we have 20 + 20 sample means and sds (sample size: 10 > observations each) drawn from 2 different populations (I mean, 20 from > population1 and 20 from population 2). Sample means and sds drawn from > population 1 are now labelled mean_alfa and sd_alfa. Sample means and sds > drawn from population 2 are now labelled mean_beta and sd_beta. Ttests are > performed under the equal variance assumption; hence, I have plugged in > pooled_variance formula (please, see v`i' line of the beneath reported Stata > 9.2/Se .do file), as from Pagano M, Gavreau K. Principles of Biostatistics. > 2nd edition. Brooks/Cole, 2000 (p 206 of the Italian edition). > Example now includes retrieving and storing two-sided p-value. > > set obs 20 > g mean_alfa=2*uniform() > g mean_beta=1*uniform() > g sd_alfa=.03*uniform() > g sd_beta=.02*uniform() > g double var_pooled=. > g double student_t=. > g double p_value=. > qui forval i = 1/20 { > qui g v`i'=((10-1)*sd_alfa[`i']^2+(10-1)*sd_beta[`i']^2)/(10+10-2) > sum v`i', meanonly > replace var_pooled=r(mean) in `i' > qui g t`i' = (mean_alfa[`i']-mean_beta[`i'])/(v`i'*(1/10+1/10))^.5 > sum t`i', meanonly > replace student_t=r(mean) in `i' > qui g w`i'=ttail(18,abs(t`i')) > sum w`i', meanonly > replace p_value=r(mean) in `i' > drop v`i' > drop t`i' > drop w`i' > } > > Again, not that elegant, but I do hope this help. > > Kind Regards, > Carlo > -----Messaggio originale----- > Da: Carlo Lazzaro [mailto:carlo.lazzaro@tiscalinet.it] > Inviato: sabato 4 luglio 2009 10.46 > A: 'statalist@hsphsun2.harvard.edu' > Cc: 'Christian Bustamante' > Oggetto: R: Mata question > > Dear Christian, > the following is a temptative answer to your query, not in Mata language. > Let's assume we have 20 + 20 sample means and sds (sample size: 10 > observations each) drawn from 2 different populations (I mean, 20 from > population1 and 20 from population 2). Sample means and sds drawn from > population 1 are labelled a and c. Sample means and sds drawn from > population 2 are labelled b and d. Ttests are performed under the equal > variance assumption. Example stops at Student t retrieving and storing for > each ttest performed (two-sided p-value was not included in the Stata .do > file). > > set obs 20 > g a==2*uniform() > g b=1*uniform() > g c=.03*uniform() > g d =.03*uniform() > g double student_t=. > qui forval i = 1/20 { > g t`i' = (a[`i']-b[`i'])/(c[`i']^2/10+d[`i']^2/10)^.5 > sum t`i', meanonly > replace student_t=r(mean) in `i' > drop t`i' > } > > Not that elegant, but I do hope this help. > > Kind Regards, > Carlo > -----Messaggio originale----- > Da: owner-statalist@hsphsun2.harvard.edu > [mailto:owner-statalist@hsphsun2.harvard.edu] Per conto di Christian > Bustamante > Inviato: sabato 4 luglio 2009 9.15 > A: Statalist > Oggetto: st: Mata question > > Hi all > > I'm trying to do a loot with a nested -ttesti- but I couldn't do it. I > have two vector with different means (m1 and m2) and another two with > each mean's standard deviation (s1 and s2). This vectors are quite > large, so do -ttesti- element for element could be very costly. Also, > I have each sample's size on two variables: n1 and n2. All this values > are obtained from a logistic regresion. After run -ttesti- I want to > save the t-statistic -r(t)- and the probability for two-sided p-value > -r(p)-. I'm doing something like this: > > forvalues i=1/size(m1) { /* how can i get vector's size? */ > ttesti n1 m1[1,`i'] s1[1,`i'] n1 m1[1,`i'] s1[1,`i'] > mat tvalues[1,`i']=r(t) > mat pvalues[1,`i']=r(p) > } > > But appears a lot of errors: 1) n1 should be integer. 2) 'm1' found > where number expected. 3) varlist not allowed. > How can I solve this? > > Thanks > > > > -- > CdeB > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > > > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > -- CdeB * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**R: st: R:R:st Mata question***From:*"Carlo Lazzaro" <carlo.lazzaro@tiscalinet.it>

**References**:**st: R:R:st Mata question***From:*"Carlo Lazzaro" <carlo.lazzaro@tiscalinet.it>

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