Applicazione Pratica Metodi per l'analisi di dati qualitativi binari
Applicazione Pratica Metodi per l'analisi di dati qualitativi binari
Applicazione Pratica Metodi per l'analisi di dati qualitativi binari
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■Calcolare <strong>per</strong> i soggetti trattati e <strong>per</strong> i soggetti non trattati le probabilità π, gli odds e i logit.Calcolare, infine, l’odds ratio dei soggetti trattati rispetto ai non trattati.tab improve treatment, col| treatmentimprove | Placebo Treated | Total-----------+----------------------+----------No | 29 13 | 42| 67.44 31.71 | 50.00-----------+----------------------+----------Yes | 14 28 | 42| 32.56 68.29 | 50.00-----------+----------------------+----------Total | 43 41 | 84| 100.00 100.00 | 100.00<strong>di</strong> "Odds(Placebo) = " 0.3256/(1-0.3256) " Logit(Placebo) = " log(0.3256/(1-0.3256))<strong>di</strong> "Odds(Treated) = " 0.6829/(1-0.6829) " Logit(Treated) = " log(0.6829/(1-0.6829))TABELLA 1:TREAT IMPROVE Total Prob Odds Logit Odds Ratio---------------------------------------------------------------------Placebo 14 43 0.3256 0.48 -0.728 1Treated 28 41 0.6829 2.15 0.767 4.48---------------------------------------------------------------------■Calcolare le probabilità π, gli odds, i logit e gli odds ratio stratificando <strong>per</strong> genere.table sex improve treatment, col------------------------------------------------------| treatment and improve| ----- Placebo ----- ----- Treated -----sex | No Yes Total No Yes Total----------+-------------------------------------------Female | 19 13 32 6 21 27Male | 10 1 11 7 7 14------------------------------------------------------<strong>di</strong> "Odds(Male,Treated) = " 0.5/(1-0.5) " Logit(Male,Treate) = " log(0.5/(1-0.5))<strong>di</strong> "Odds(Male,Placebo) = " 0.0909/(1-0.0909) " Logit(Male,Placebo) = " log(0.0909/(1-0.0909))<strong>di</strong> "Odds(Female,Treated) = " 0.778/(1-0.778) " Logit(Female,Treated) = " log(0.778/(1-0.778))<strong>di</strong> "Odds(Female,Placebo)= " 0.4062/(1-0.4062) " Logit(Female,Placebo) = " log(0.4062/(1-0.4062))TABELLA 2:SEX TREAT IMPROVE Total Prob Odds Logit------------------------------------------------------------------Female Treated 21 27 0.7778 3.50 1.2529Female Placebo 13 32 0.4062 0.68 -0.3797Male Treated 7 14 0.5000 1.00 0.0000Male Placebo 1 11 0.0909 0.10 -2.3026------------------------------------------------------------------Il modello <strong>di</strong> regressione logistica esprime il logit del soggetto j come funzione lineare dellevariabili esplicative:(j) = α + β1TREATMENTjlogit π (1)2