Hi
> -----Original Message-----
> From: r-help-boun...@r-project.org [mailto:r-help-bounces@r-
> project.org] On Behalf Of meng
> Sent: Sunday, March 10, 2013 5:33 AM
> To: Greg Snow
> Cc: R help
> Subject: Re: [R] quesion about lm function
>
> Thanks for your reply.
> But the mean y of sex(f) and sex(m) can't be negative since the min and
> max of y is 1632.5 and 6410.6 respectively.
>
> And your code's result:
>
> sex(f): -1255.56
> sex(m):-1118.73
>
> The above result isn't correct since they are negative.
You did not read the full advice.
> The tests are likely to be meaningless in this case and the means are
> the predicted means at x1=0 and x2=0 (so the means may make more sense
> if x1 and x2 are centered first).
The above results (means) are correct at x1 and x2 = 0.
result_lm <- lm(y~0+factor(sex) + scale(x1) + scale(x2), data=test)
coef(result_lm)
factor(sex)f factor(sex)m scale(x1) scale(x2)
3876.6290 4013.4576 945.5634 592.7385
Anyway not a big difference from
tapply(test$y, test$sex, mean)
f m
3790.760 4099.327
Regards
Petr
>
> Thanks
>
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> At 2013-03-10 02:39:21,"Greg Snow" <538...@gmail.com> wrote:
>
> You can get the 2 means with:
>
>
> result_lm <- lm(y~0+factor(sex) + x1 + x2)
>
>
> The tests are likely to be meaningless in this case and the means are
> the predicted means at x1=0 and x2=0 (so the means may make more sense
> if x1 and x2 are centered first).
>
>
>
> On Sat, Mar 9, 2013 at 3:35 AM, meng <laomen...@163.com> wrote:
> Hi all:
> My data is in the attachment.
> I want to analysis the mean difference of y between 2 sex.
>
> My code:
> result_lm<-lm(y~factor(sex) + x1 + x2)
> summary(result_lm)
>
> The result of "factor(sex)m" 136.83, is the mean difference of y
> between 2 sex,and the corresponding p value is 0.07618.
>
> My question is: how to get the mean y of sex(m) and sex(f) respectively
> via lm function?
>
> Many thanks for your help.
> My best.
>
>
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> --
> Gregory (Greg) L. Snow Ph.D.
> 538...@gmail.com
> [[alternative HTML version deleted]]
>
> ______________________________________________
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