Engineers are interested in comparing the mean hydrogen production rates per day for three different heliostat sizes. From the past week’s records, the engineers obtained the amount of hydrogen produced per day for each of the three heliostat sizes. Then they computed and compared the sample means, which showed that the mean production rate per day increased with the heliostat sizes. a. Identify the type of the study describe here. b. Discuss the type of interference that can and cannot be drawn from this study.
1. Engineers are interested in comparing the mean hydrogen production rates per day for three
different heliostat sizes. From the past week’s records, the engineers obtained the amount of
hydrogen produced per day for each of the three heliostat sizes. Then they computed and
compared the sample means, which showed that the mean production rate per day increased
with the heliostat sizes.
a. Identify the type of the study describe here.
b. Discuss the type of interference that can and cannot be drawn from this study.
2. To investigate reasons why people do not work, the Census Bureau interviewed a group of
randomly selected individuals, from April-July 1996, in four separate rotation groups,
respondents were asked to select 1 of 11 categories consisting of economic and noneconomic
reasons for not working, in response to the question, “What is the main reason you did not work
at a job or business [in the last four months]?”
a. Identify the type of the study described here.
b. Identify the population of interest.
3. Ariatnam, Najafi, and Morones (Journal of professional Issues in Engineering Education and
Practice, 2002) describe an overview of academies in horizontal directional drilling conducted to
train engineers and inspector for the California Department of Transportation. A pretest was
administered on the first day prior to any instruction. Instruction and field experience were
provided over a 3 day period, followed by a final test administered at the end of the last day.
Although the average final test score of 75.27% was higher than the average pretest score of
55.61%, the difference was not significant.
a. Identify the type of the study described here.
b. What is the purpose of administering the pretest?
4. A materials engineer wants to study the effects of two different processes for sintering copper (a
process by which copper powder coalesces into a solid but porous copper) on two different types
of copper powders. From each type of copper powder, she randomly selects two samples and
then randomly assigns one of the two sintering processes to each sample by the flip of a coin.The response of interest measured is the porosity of the resulting copper. Explain what type of
study this is and why.
5. A textile engineer is interested in measuring heat resistance of four different types of treads used
in making fire-resistant clothing for firefighters. A random sample of 20 threads from each type
was taken and subjected to a heat test to determine resistance (the length of time the fibers survive
before starting to burn.) Explain what type of study this is and why.
6. A manufacturer of “Keep it Warm” bags is interested in comparing the heat retention of bags
when used at five different temperatures (100 oF, 125 oF, 150 oF, 175 oF, and 200 oF). Thirty bags
are selected randomly from last week’s production and randomly assigned, six each, to five
different groups. Items from group 1 at beginning temperature 100 oF were kept in bags for an
hour, and the temperatures of those items were recorded after an hour. Similarly, groups 2 to 5
were assigned items at 125 oF, 150 oF, 175 oF, and 200 oF, respectively.
a. Identify the type of study used here.
b. What type of inference is possible from this study?
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