[R] How to predict the mean and variance of the dependent variable after regression

[Joshua Wiley]

Hello,

If you just want the mean and variance of log(y) try:

mean(log(y))
var(log(y))

if there is missing data, you can add na.rm=TRUE to both of those.  If
you want the mean and variance of the predicted ys

mean(predict(linmod))
var(predict(linmod))

see

?mean
?var
?predict.lm #the specific method being used for predict() with model
objects of class lm

HTH,

Josh

On Mon, Jun 21, 2010 at 11:24 AM, Yi <liuyi.feier at gmail.com> wrote:
> Hi, folks,
>
> As seen in the following codes:
>
> x1=rlnorm(10)
> x2=rlnorm(10,mean=2)
> y=rlnorm(10,mean=10)### Fake dataset
> linmod=lm(log(y)~log(x1)+log(x2))
>
> After the regression, I would like to know the mean of y. Since log(y) is
> normal and y is lognormal, I need to know the mean and variance of log(y)
> first.  I tried mean (y) and mean(linmod), but either one is what I want.
>
> Any tips?
>
> Thanks in advance!
>
>        [[alternative HTML version deleted]]
>
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-- 
Joshua Wiley
Ph.D. Student
Health Psychology
University of California, Los Angeles