given a different feed supplement. You are to analyze how the
weight
(grams, after six
weeks) of a chick depends on the
feed
that it was assigned.
(a)
[2 pts] Fit an appropriate ANOVA model. Display a summary of your results.
1
Even though
sex
is a categorical variable, it can be used as a numerical predictor here because it has only two
levels, and they are numerically encoded.

1

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(b)
[2 pts] Produce an ANOVA table.
(c)
[2 pts] Test whether there are any differences among the mean weights of the groups
(based on an
F
-test at
α
= 0
.
05).
(d)
[2 pts] Produce Tukey simultaneous 95% confidence intervals for all mean differences
between pairs of groups.
(e)
[2 pts] According to your Tukey intervals, which pairs of feeds have significantly
different means (after adjusting for multiple comparisons)?
(f)
[2 pts] Produce the usual diagnostic plots for your model, and draw conclusions.
4.
[GRADUATE STUDENTS ONLY] The data set
infmort
contains data on infant mortality
in 105 nations,
2
along with their per capita income and a factor indicating whether or not
they export oil.
(a)
[2 pts] Fit the regression of
log(mortality)
on
log(income)
and
oil
. Give a
summary of the results. Is
oil
significant?
(b)