Step-by-step solutions to hundreds of study design questions - PlainMath

Recent questions in Study design

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asked 2021-08-14

The pathogen Phytophthora capsici causes bell pepper plants to wilt and die. A research project was designed to study the effect of soil water content and the spread of the disease in fields of bell peppers. It is thought that too much water helps spread the disease. The fields were divided into rows and quadrants. The soil water content (percent of water by volume of soil) was determined for each plot. An important first step in such a research project is to give a statistical description of the data.
Soil Water Content for Bell Pepper Study
\(\begin{array}{cc} 15&14&14&14&3&12&11&11&11&11&10&11&13&16&10\\ 9&15&12&9&10&7&14&13&14&8&9&8&11&13&13 \\ 15&12&9&10&9&9&16&16&12&10&11&11&12&15&8\\ 10&10&10&11&9 \end{array}\)
(a) Make a box-and-whisker plot of the data. Find the interquartile range.

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asked 2021-08-12

State whether the investigation in question is an observational study or a designed experiment. Justify your answer in each case.In the 1940s and early 1950s, the public was greatly concerned about polio. In an attempt to prevent this disease, Jonas Salk of the University of Pittsburgh developed a polio vaccine. In a test of the vaccine’s efficacy, involving nearly 2 million grade-school children, half of the children received the Salk vaccine. the other half received a placebo, in this case an injection of salt dissolved in water. Neither the children nor the doctors performing the diagnoses knew which children belonged to which group, but an evaluation center did. The center found that the incidence of polio was far less among the children inoculated with the Salk vaccine. From that information, the researchers concluded that the vaccine would be effective in preventing polio for all U.S. school children. consequently, it was made available for general use.

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asked 2021-08-11

A survey was designed to study how business operations vary according to their size. Companies were classified as small, medium, or large. Questionnaires were sent to 200 randomly selected businesses of each size. Because not all questionnaires were returned, researchers decided to investigate the relationship between the response rate and the size of the business. The data are given in the two-way table.
\(\text{Business size} \\ \begin{array}{l|r|r|r|r} && \text { Small } & \text { Medium } & \text { Large } & \text { Total } \\ \hline \text{Response?} & \text { Yes } & 125 & 81 & 40 & 246 \\ \hline &\text { No } & 75 & 119 & 160 & 354 \\ \hline &\text { Total } & 200 & 200 & 200 & 600 \end{array}\)
Which variable should be used as the explanatory variable? Explain.

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asked 2021-08-10

In a study designed to investigate the effects of a strong magnetic field on the early development of mice, ten cages, each containing three 30-day-old albino female mice, were subjected for a period of 12 days to a magnetic field having an average strength of 80 Oe/cm. Thirty other mice, housed in ten similar cages, were not put in the magnetic field and served as controls. Listed in the table are the weight gains, in grams, for each of the twenty sets of mice.
\(\begin{array}{cccc} \text { Cage } & \text { Weight Gain (g) } & \text { Cage } & \text { Weight Gain (g) } \\ \hline 1 & 22.8 & 11 & 23.5 \\ 2 & 10.2 & 12 & 31.0 \\ 3 & 20.8 & 13 & 19.5 \\ 4 & 27.0 & 14 & 26.2 \\ 5 & 19.2 & 15 & 26.5 \\ 6 & 9.0 & 16 & 25.2 \\ 7 & 14.2 & 17 & 24.5 \\ 8 & 19.8 & 18 & 23.8 \\ 9 & 14.5 & 19 & 27.8 \\ 10 & 14.8 & 20 & 22.0 \\ \hline \end{array}\)
Test whether the variances of the two sets of weight gains are significantly different. Let α=0.05. For the mice in the magnetic field, \(s_X=5.67\). for the other mice, \(s_Y=3.18\)

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asked 2021-07-04

An experiment designed to study the relationship between hypertension and cigarette smoking yielded the following data. \(\begin{array}{|c|c|} \hline Tension\ level & Non-smoker & Moderate\ smoker & Heavy\ smoker \\ \hline Hypertension & 20 & 38 & 28 \\ \hline No\ hypertension & 50 & 27 & 18 \\ \hline \end{array}\)

Test the hypothesis that whether or not an individual has hypertension is independent of how much that person smokes.

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asked 2021-07-02

Do piano lessons improve the spatial-temporal reasoning of preschool children? A study designed to investigate this question measured the spatial-temporal reasoning of a random sample of 34 preschool children before and after 6 months of piano lessons. The differences (After - Before) in the reasoning scores have mean 3.618 and standard deviation 3.055.

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asked 2021-06-24

State whether the investigation in question is an observational study or a designed experiment. Justify your answer in each case. The National Association of Colleges and Employers (NACE) compiles information on salary offers to new college graduates and publishes the results in Salary Survey.

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asked 2021-06-24

What are the treatments for a designed study that utilizes one qualitative factor with four levels: A, B, C, and D?

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asked 2021-06-22

A bank wants to know which of two incentive plans will most increase the use of its credit cards. It offers each incentive to a group of current credit card customers, determined at random, and compares the amount charged during the following six months. What type of study design is being used to produce data?

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asked 2021-06-20

State whether the investigation in question is an observational study or a designed experiment. Justify your answer in each case.In the 1940s and early 1950s, the public was greatly concerned about polio. In an attempt to prevent this disease, Jonas Salk of the University of Pittsburgh developed a polio vaccine. In a test of the vaccine’s efficacy, involving nearly 2 million grade-school children, half of the children received the Salk vaccine; the other half received a placebo, in this case an injection of salt dissolved in water. Neither the children nor the doctors performing the diagnoses knew which children belonged to which group, but an evaluation center did. The center found that the incidence of polio was far less among the children inoculated with the Salk vaccine. From that information, the researchers concluded that the vaccine would be effective in preventing polio for all U.S. school children; consequently, it was made available for general use.

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asked 2021-06-20

Define the following terms: a. Observational study, b. Designed experiment.

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asked 2021-06-18

Who is more likely to binge drink—male or female college students? The Harvard School of Public Health surveys random samples of male and female undergraduates at four-year colleges and universities about whether they have engaged in binge drinking. What type of study design is being used to produce data?

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asked 2021-06-16

Refer to the Journal of Experimental Social Psychology (Vol. 45, 2009) study of whether buying gifts truly buys love. Recall that study participants were randomly assigned to play the role of gift giver or gift receiver. Gift receivers were asked to provide the level of appreciation (measured on a 7-point scale where 1 = "not at all" and 7 = "to a great extent") they had for the last birthday gift they received from a loved one. Gift givers were asked to recall the last birthday gift they gave to a loved one and to provide the level of appreciation the loved one had for the gift. The researchers wanted to know if the average level of appreciation is higher for birthday gift givers than for birthday gift receivers. a. Why is this study designed? b. Specify the key elements of the study: experimental unit, response variable, factor, and treatments.

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asked 2021-06-15

Determine whether the study is an observational study or an experiment. Explain. In a study designed to research the effect of music on driving habits, 1000 motorists ages 17- 25 years old were asked whether the music they listened to influenced their driving.

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asked 2021-06-10

Can filling car tires with nitrogen instead of compressed air increase gas mileage? Describe how you would design a study to try to answer this question. Be as specific as you can about the details of your study.

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asked 2021-06-07

Smoking and drinking coffee have a tendency to stain teeth. In an effort to determine the ability of chewing gum to remove stains on teeth, researchers conducted an experiment in which 64 bovine incisors (teeth) were stained with natural pigments such as coffee for 10 days. Each tooth was randomly assigned to one of four treatments: gum A, gum B, gum C, or saliva. Ea ch tooth group was placed into a device that simulated a human chewing gum. The temperature of the device was maintained at body temperature and the tooth was in the device for 20 minutes. The process was repeated six times (for a total of 120 minutes of chewing). The researcher conducting the experiment did not know which treatment was being applied to each experimental unit. Upon removing a tooth from the chewing apparatus, the color change was measured using a spectrophotometer. The percent age of stain removed by each treatment after 120 minutes is as follows: Gum A, 47.6%; Gum B, 45.2%, Gum C, 21.4%, Saliva, 2.1%. The researchers concluded that gums A and B removed significantly more stain than gum C or saliva. In addition, gum C removed significantly more stain than saliva. (a) Identify the research objective. (b) Is this an observational study or designed experiment? Why? (c) If observational, what type of observational study is this? If an experiment, what type of experimental design is this? (d) What is the response variable? (e) What is the explanatory variable? ls it qualitative or quantitative? (I) Identify the experimental units. (g) State a factor that could affect the value of the response variable that is fixed at a set level. (h) What is the conclusion of the study?

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asked 2021-06-03

The American Journal of Political Science (Apr. 2014) published a study on a woman's impact in mixed-gender deliberating groups. The researchers randomly assigned subjects to one of several 5-member decision-making groups. The groups' gender composition varied as follows: 0 females, 1 female, 2 females, 3 females, 4 females, or 5 females. Each group was the n randomly assigned to utilize one of two types of decision rules: unanimous or majority rule. Ten groups were created for each of the \(6\ \times\ 2=12\) combinations of gender composition and decision rule. One variable of interest, measured for each group, was the number of words spoken by women on a certain topic per 1,000 total words spoken during the deliberations. a. Why is this experiment considered a designed study? b. Identify the experimental unit and dependent variable in this study. c. Identify the factors and treatments for this study.

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asked 2021-06-01

Determine whether the study depicts an observational study or a designed experiment. Identify the response variable in each case. A sport s report er asks 100 baseball fans if Barry Bonds's 756th homerun ball should be marked with an asterisk when sent to the Baseball Hall of Fame.

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asked 2021-05-22

In a study designed to investigate the effects of a strong magnetic field on the early development of mice, ten cages, each containing three 30-day-old albino female mice, were subjected for a period of 12 days to a magnetic field having an average strength of 80 Oe/cm. Thirty other mice, housed in ten similar cages, were not put in the magnetic field and served as controls. Listed in the table are the weight gains, in grams, for each of the twenty sets of mice. \(\scriptstyle \begin{array}{c} \hline \text { In Magnetic Field } & \text { Not in Magnetic Field } \\ \hline\end{array} \scriptstyle\begin{array}{cccc} \text { Cage } & \text { Weight Gain (g) } & \text { Cage } & \text { Weight Gain (g) } \\ \hline 1 & 22.8 & 11 & 23.5 \\ 2 & 10.2 & 12 & 31.0 \\ 3 & 20.8 & 13 & 19.5 \\ 4 & 27.0 & 14 & 26.2 \\ 5 & 19.2 & 15 & 26.5 \\ 6 & 9.0 & 16 & 25.2 \\ 7 & 14.2 & 17 & 24.5 \\ 8 & 19.8 & 18 & 23.8 \\ 9 & 14.5 & 19 & 27.8 \\ 10 & 14.8 & 20 & 22.0 \\ \hline \end{array}\)

Test whether the variances of the two sets of weight gains are significantly different. Let \(\alpha=0.05\ \alpha=0.05\). For the mice in the magnetic field, \(sX=5.67\); for the other mice, \(sY=3.18\)

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asked 2021-05-22

Are Toyota or Nissan owners more satisfied with their vehicles? Let’s design a study to find out. We’ll select a random sample of 400 Toyota owners and a separate random sample of 400 Nissan owners. Then we’ll ask each individual in the sample: “Would you say that you are generally satisfied with your (Toyota/Nissan) vehicle?” What type of study design is being used to produce data?

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