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From |
"Carlo Lazzaro" <carlo.lazzaro@tiscalinet.it> |

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

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

Date |
Sun, 5 Jul 2009 12:26:20 +0200 |

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/

**Follow-Ups**:**Re: st: Mata question***From:*"Joseph Coveney" <jcoveney@bigplanet.com>

**Re: st: R:R:st Mata question***From:*Christian Bustamante <cdeb77@gmail.com>

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