Biological Statistics II
Biometry 3020 / Natural Resources 4130 / Stat Sci 3200
Homework 2
Due on Thursday February 11
1.
Now that you are familiar with the grade point average data consider the
diagnostics problem KNNL 3.3, do all components of this problem except
for part e that uses the BrownForsythe test, which we did not cover in
class. Note use a stemandleaf plot in place of doing a dot plot.
a.
(2 points) Prepare a box plot for the ACT scores
i
X
. Are there any
noteworthy features in this plot?
boxplot(CH01PR19$ACT)
b.
(2 points) Prepare a stemandleaf plot of the residuals. What
information does this plot provide?
stem(resid(GPA.lm))
c.
(2 points) Plot the residual
i
e
against the fitted values
i
Y
ˆ
. What
departures from regression model (2.1) can be studied from this
plot? What are your findings?
d.
(2 points) Prepare a normal probability plot (quantile plot) of the
residuals. Also obtain the coefficient of correlation between the
ordered residuals and their expected values under normality. Test
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 Spring '10
 SULLIVAN
 Normal Distribution, Errors and residuals in statistics, residuals, Statistical charts and diagrams, stemandleaf plot, Normal probability plot

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