STAT 100 Midterm 2a
INSTRUCTIONS: Answer all questions on all pages. Write your answers clearly in the spaces
provided. Where computations are required, you should show work. Incorrect answers without
clearly-displayed work cannot be considered for partial credit. If a question calls for an
explanation, provide one that is complete. Do not omit important details or include irrelevant or
incorrect statements. True/False or multiple choice questions need not be accompanied by an
If you have difficulty, or feel like you are working slowly, solve the easiest problems first.
Total points on exam:
“All of these liars and cheats and thieves are graduates of our
Robert Gates, President of Texas A & M University, in his inaugural speech referring to recent
scholarly, corporate and political corruption. STAT 100 Midterm 1, Fall 2009
QUESTION 1 (8 pts)
Insects grow at rates that depend on the temperature: the warmer it is, the faster they grow.
Experiments are often run to study how the growth rate of a particular species of insect depends
on temperature. Growth rate is defined in terms of how much insects grow in one day. A
straight line regression model is used to represent the relationship between temperature and
growth rate. One particular experiment was run studying insects raised at different temperatures
ranging between 15C-35C. The regression equation was y = -11.2 + 0.95 x. The RMSE was
0.96 and the R was 0.49. A visual inspection of the scatterplot indicated that a straight line was
a reasonable model.
A. (1 pt) For this regression, what variable would be “x” and what variable would be “y”?
B. (1 pt) Explain what -11.2 measures in terms of the insects.
C. (1 pt) Explain what 0.95 measures in terms of the insects.
D. (1 pt) The average temperature in the summer where these insects live is about 20C.
Predict the growth rate at that temperature.
a. (1 pt) Within what interval would you expect about 95% of insects’ growth rates
E. (1 pt) This species is actually a helpful insect. Another environment where people are
considering importing this insect has an average temperature of 10C during the time
when these insects could do the most good. Predict the growth rate at that temperature.
a. (1 pt) Comment on why this should not be expected to be a reliable prediction.
F. (1 pt) What is the correlation between temperature and growth rate?
2 STAT 100 Midterm 1, Fall 2009
QUESTION 2 (4 pts)
Political idology vs. gender in US voters, 1991
Female Very Conservative
0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0
The chart above is based on data from a 1991 survey of 832 U.S. voters who identified their own
political ideology. Note that the categories in the bars are in the same order as in the legend.
A. (1 pt) For each gender,