Stat 311 Summer 2022 Quiz 1
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Quiz 1 consists of three equally weighted problems, due uploaded to Gradescope by 11:30 PM PDT July
12th. Do not wait until the last minute to upload as no late quizzes will be allowed.
The quiz is written for about 1 hour and 45 minutes assuming you studied but you may complete the quiz
anytime during the open window (since there is so much supplementary material for Problems 1 and 2, I
decided to not have a timed quiz); just be sure to leave yourself time to upload your answers before the
deadline.
This quiz is open Stat 311 notes, textbook, homework and posted supplementary materials only. All
responses must be your own. Do not make be regret giving an untimed quiz—if I suspect that you
collaborated with other people or put down answers that match something you found on the internet, your
quiz score will be zero and I will file a report with the Student Conduct office. By uploading your quiz to
Gradescope, you are acknowledging that you adhered to the rules and academic conduct standards set by
the University of Washington.
Pay attention to sentence or word length requirements. We will not read more than the allowed limits.
Also, always keep context in mind and report units when applicable.
If you have questions about any of the questions, you may post a private message on Ed Discussion. Do
note that I can only guarantee responses during daytime hours on Monday and Tuesday. I will not answer
any questions after 5 PM PDT on Tuesday, July 12th.
Problem 1 (10 points): Read the short UW News article for an overview of a study that showed that areas
with historical redlining were associated with more air pollution. Then look at the published journal article
that provides more details about the study. The news and journal articles can be found in the Quiz 1
assignment on Canvas. Use information in these articles to answer parts (a) – (g). Except for part (f), limit
your responses to at most two sentences.
a) Was this an experiment or observational study. Briefly explain. (0.5 point)
b) What is meant by the term redlining that is used in the two articles? (1 point)
c) What were the main sources of data for this study? (0.5 point)
d) Race and ethnicity were combined into which aggregate groups for this study? Include the HOLC
percentages of each group. (2 points)
e) What are the main two pollutants that were investigated in this study and why did they focus on just
these two? (1 point)
f) Figure 1 of the journal article shows population weighted distributions for both pollutants. Summarize
what you can glean from the top left plot [Unadjusted NO2 national aggregation]. Be sure to speak to
the HOLC grades and race/ethnicity. Limit your response to at most 150 words. (3 points)
g) Figure 2 in the journal article looks at the interaction between racial/ethnic groups and historical
redlining grades. What does the right plot (PM2.5 difference) tell you about the association between
these two variables? (2 points)
Stat 311 Summer 2022 Quiz 1
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Problem 2 (10 points): Five measurements were taken on two species of fish from a single lake (?? = 35
Bream and ?? = 33 Perch). For this problem, fish weight is the response (??) and cross length, height and
diagonal width are predictors of fish weight. This problem does not require any coding; rather, we are
providing summary graphs, summary tables, and lm output in the supplementary handout,
Quiz1Problem2.pdf, posted in the Quiz 1 assignment on Canvas. Use the information in this handout to
answer parts (a) – (g).
a) Look at the density plot in the last row of Figure 2 and the histograms in Figure 6 of the supplementary
handout (pages 3 and 7) and describe the overall distribution of the observed sample widths. Also
compare the sample distributions for widths individually for Bream and Perch. Use no more than four
sentences. (1.5 points)
b) Look at Figure 2 (page 3) of the supplementary handout and interpret the overall joint relationship for
Weight on Width. Also comment on the relationship when considering species. [Hint: make clear,
specific observations regarding the relationships]. Use no more than three sentences. (1.5 point)
c) Using Figure 2 (page 3), what is the overall sample correlation between Height and Width. What are
the correlations for Height and Width by species? How do correlations by species compare with the
overall correlation? Use no more than two sentences. (2 points)
d) Write out the regression equation for Weight on Height. In one sentence, interpret the estimated
slope parameter for this regression in the context of the problem. (1 point)
e) Report and in one sentence interpret the coefficient of determination for the regression of Weight on
Length3 in the context of the problem. (1 point)
f) We have provided the output for simple linear regressions of Weight on the three predictor variables
we are considering. Of the three models, which model do you think is the best single predictor model?
Use all the information (scatterplots, lm outputs, residual plots, and histograms of the residuals) to
support your choice. We are looking for written answers that are in the context of the problem and that
you support your choice with more than a single piece of information. Limit your answer to a
maximum of 100 words. You may use bullet points if that helps you organize your answer. (2 points)
g) On pages 12 and 13 of the supplementary handout, we provide regression output that includes Width
and the additional categorical variable Species. Of the three models for Weight on Width (single
regression all species, differing intercepts by species (parallel lines), or different slopes by species),
which model do you think is best? Use the information from the regression outputs and Figure 7 to
justify your answer. Limit your answer to at most three sentences. (1 point)
Stat 311 Summer 2022 Quiz 1
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Problem 3 (10 points; 2 points each): True or False. If the statement is True, then indicate True. If the
statement is False, then indicate False and carefully explain with no more than three sentences why the
statement is false.
a) A researcher is interested in administering a survey to gauge attitudes of Catholic Church members
regarding the current Pope. A random sample of five Catholic Churches in King County are selected and
all church members of those five churches are surveyed. This type of sample is called a stratified sample.
b) A student is collecting data on movie preferences for a class project. The student stands outside a
neighborhood theater and asks people exiting the theater if they would be willing to take a brief survey.
The student can get 50 people willing to participate over the course of six hours. The 50 completed
surveys are an example of a simple random sample.
c) A study compared a group of men who had heart attacks with a similar group of controls. The
proportion of men with male pattern baldness was compared between the two groups. This is an
example of an observational study.
d) A sample of households in a community is selected at random from the telephone directory. In this
community, 4% of households have no telephone, 10% have only cell phones, and another 25% have
unlisted telephone numbers. The largest issue with this sampling scenario is response bias.
e) The contingency table shown below is from a Pew Research Center study, published in May 2022, that
looked at use of video conferencing services (Zoom, Webex or other) for three levels of work from
home status.
Work from home
status
Use of Video Conferencing for Work
Often Sometimes Hardly Ever Never Total
All or most of the time 66 17 7 11 101
Sometimes 49 28 16 7 100
Rarely or never 35 30 18 17 100
Total 150 75 41 35 301
The joint percentage of people that sometimes work from home and never use video conferencing for
work is 2.3% (rounded to one decimal place), and among people that sometimes use video
conferencing for work, 16.8% (rounded to one decimal place) work from home all or most of the time,
28% sometimes work from home and 30% rarely or never work from home.