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st: RES: Dummy


From   "Henrique Neder" <hdneder@ufu.br>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RES: Dummy
Date   Sun, 2 Dec 2007 17:49:22 -0200

Linda

In some form you can use a dummy as a dependent variable in logistic model
or in a probit model. These models are non linear and through them you can
estimate the probability of a particular event. This event is relative a
dichotomous variable (1 = success, 0 = failure). The logit model is of form:

Ln(p/(1-p)) = beta0 + beta1*X1 + beta2*X2 + ... + betap*Xp + u

where:

p = probability of sucess
beta0, beta1, ..., betap are parameters
X1, X2, ...., Xp are covariates (independent variables).
u is the error term

p/(1-p) is the odd ratio and p = probability of X = 1. So you are modeling
not X directly, but the probability of X assuming a determinate value. X is
a dummy variable.
The interpretation of the parameters (estimates) values are as follow:

If the estimate of betap is betaphat so a variation of one unity in Xp
"cause" a variation of 100*(exp(betaphat)-1) per cent in the odd ratio
(p/(1-p)), fixing the others covariates. This is somehow different of the
multiple regression estimates in a linear model.    
 
Henrique
    

-----Mensagem original-----
De: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] Em nome de Linda Walker
Enviada em: sábado, 1 de dezembro de 2007 14:30
Para: statalist@hsphsun2.harvard.edu
Assunto: st: Dummy

Hello statalist

Can dummy(ies) be used as dependent variable(s)? Please help.

Many thanks

Linda

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