[R] Is this correct?

Bill.Venables at csiro.au Bill.Venables at csiro.au
Mon Nov 24 05:50:19 CET 2008

R help does have guidelines.  (See the bottom of any message to R help, including yours.)  Here is a relevant extract from them:

"Basic statistics and classroom homework: R-help is not intended for these."

Your questions are entirely inappropriate.

It would also be courteous if we knew your name and not just an alias.

Bill Venables

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Rlover
Sent: Monday, 24 November 2008 12:46 PM
To: r-help at r-project.org
Subject: [R] Is this correct?

I have to answer the following question for a homework assignment.

A researcher was interested in whether people taking part in sports at
university made more money after graduating, taking into account the
students' GPA. They sampled 200 alumni from a large university. The
variables are: income (income 10 years after graduating), sports (1 if they
did sports, 0 if they did not), and GPA (the grade point average at
university). Discuss the relationship between taking part in sports, GPA,
and income for these data.

The R code I used so far is

Does sports predict GPA?

> lm1<-lm(GPA~sports)
> summary(lm1)

Does sports predict income?
> lm2<-lm(income~sports)
> summary(lm2)

Does GPA predict income?
> lm3<-lm(income~GPA)
> summary(lm3)

Does sports predict income after accounting for GPA?
> lm4<-lm(income~GPA+sports)
> summary(lm4)

Can someone let me know is the above is correct? I am not sure if to keep
all four regressions or only 1 and 4. Also, I need to plot the data on a
graph or table. Can anyone suggest how to do this? Thank you in advance :)

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