Stat 301
HW 4
Due: 25 Sept / 28 Sept 2015
Readings for material covered on midterm 1:
1.1-1.5, skim 1.6, 1.8-1.10, 2 (all), 3.1-3.6, 3.9-3.10, 7.1-7.2
1. Text problem 1.106 (p. 77). The data are provided two ways: fmattitudes.txt has one row for
each student. fmattitudes2.csv has one row for each observation. You need to decide which
is the appropriate data set to analyze.
Answer the book’s questions, followed by my question (c).
Note: In (a), the book is asking you to state the null and alternative hypotheses.
(c) Report a 95% confidence interval for the mean difference in attitude between fathers and
mothers.
Each of the next three problems gives you a short description of a study. For each, decide whether
or not it is appropriate to express the study results as causal conclusions. Briefly explain your
answer.
2. An evaluation of the effectiveness of the “Spiegel” anti-smoking program. 52 smokers in
Polk County volunteered for the study. Each smoker was randomly assigned to one of two
treatments: the “Spiegel” method and a control. Each smoker was asked to record the number
of cigarettes smoked over the course of a month.
3. An evaluation of the effect of neighborhood poverty on reading proficiency. Census data are
used to construct a list of all neighborhoods in Iowa with average income near the poverty
line (poor) and a list of all neighborhoods in Iowa with average income more than twice the
national average (rich). Ten neighborhoods are randomly chosen from each list. The average
reading proficiency of 5’th grade students is measured in each of the 20 selected neighborhoods.
4. An evaluation of methods to measure the fat content of pieces of meat. Twenty pieces of
meat are randomly sampled from a processing line at a slaughterhouse. Each piece of meat
is divided into two sections. One of those sections is randomly selected to be measured by
method A. The other section is measured by method B.
5. Text problem 3.13 (p. 102). These data come from one brand of orange juice. Answer the
book’s questions, then continue with:
(d) Estimate a 95% confidence interval for the regression slope
(e) Do these data provide evidence on an association between pectic and sweetness in this
brand of OJ? Briefly explain why or why not.
(f) Is it appropriate to conclude from these data that sweetness is caused the pectin level?
Briefly explain why or why not.
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(g) Consider two production runs from this manufacturer. Estimate the average difference
in sweetness when the two runs differ by 150 ppm pectin. Or, if it is not possible to
make an appropriate estimate, explain why.
(h) The manufacturer can manipulate the production process to decrease the pectin level.
The process changes only the pectin amount. Estimate the increase in sweetness when
the manufacturer decreases the pectin concentration by 150 ppm. Or, if it is not possible
to make an appropriate estimate, explain why.
(i) You want to describe the sweetness for a single production run with a pectin concentration of 250 ppm. Calculate and report the prediction and an appropriate 95% interval.
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