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Exam 3: Gathering Data

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Question 41

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Which is important in designing a good experiment? I. Randomization in assigning subjects to treatments. II. Control of potentially confounding variables. III. Replication of the experiment on a sufficient number of subjects.

A) I and III
B) I, II, and III
C) I and II
D) I only
E) II and III

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Question 42

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To check the effect of cold temperatures on the battery's ability to start a car researchers purchased A battery from Sears and one from NAPA. They disabled a car so it would not start, put the car in a Warm garage, and installed the Sears battery. They tried to start the car repeatedly, keeping track of The total time that elapsed before the battery could no longer turn the engine over. Then they Moved the car outdoors where the temperature was below zero. After the car had chilled there for Several hours the researchers installed the NAPA battery and repeated the test. Is this a good Experimental design?

A) No, because they should have tested other brands of batteries, too.
B) Yes
C) No, because they should have tested more temperatures.
D) No, because temperature is confounded by brand.
E) No, because the car and the batteries were not chosen at random.

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Question 43

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A tree farmer hires a botanist to evaluate a blight that seems to be affecting his trees. The trees are planted in horizontal rows on a hill and the blight seems to be a bigger problem near the bottom of the hill. The farmer wants to know the extent of the damage to the trees. Since the trees must be destroyed to examine them, the botanist doesn't have time to examine all the trees, so she will select a sample. Several plans for choosing the sample are proposed. a. Randomly select three trees from each horizontal row. b. Lay out a grid on a map of the hill. Randomly select eight squares from the grid, and check all trees in those squares. c. Randomly pick a number from 1 to 30. Start at the tree at that position in the first row, then go to every 30th tree after that. d. Check the ten trees closest to the parking lot where the botanist parks her car. -Explain why the last plan suggested above, selecting the ten trees closest to the parking lot, might be biased. Be sure to name the kind(s) of bias you describe and link it to the variable of interest.

Which of these is not an advantage of using a stratified sample instead of a simple random sample?

Political math A recent study by Yale professors found that people's ability to do mathematics computations got worse when the result went against the person's political ideology. This was based on a randomized experiment in which people were given the same basic computation, but some were given the question in a politically neutral context and others were given the same computation in a context in which the correct answer went against their political ideology. The difference between the proportion of people who got the question wrong in a 'neutral' context and those who got the question wrong in a 'political' context was reported to be "statistically significant." a. Briefly explain what "statistically significant" means in this context. b. Would it be appropriate for the news media to report that the political context caused the poor computational results? Explain.

For a school project, Max must design a survey. For his survey he plans to randomly select families and gather information about all the children in each of those families. He must have at least 20 children in his sample. The number of children per family in the U.S. is given in the table below. How many families should Max expect to survey to reach at least 20 children? (treat "5 or more" as 5.) $\begin{array} { | l | l | l | l | l | l | l | } \hline \text { No. of Children } & 0 & 1 & 2 & 3 & 4 & 5 \text { or more } \\\hline \% \text { of families } & 17 & 23 & 25 & 16 & 10 & 9 \\\hline\end{array}$ -Describe how you will use a random number table to conduct this simulation.

Administrators at a large hospital are concerned about the possibility of drug abuse by people who work there. They decide to check on the extent of the problem by having a random sample of the employees undergo a drug test. Several plans for choosing the sample are proposed. a. There are four employee classifications: doctors, medical staff (nurses, technicians, etc.) office staff, and support staff (custodians, maintenance, etc.). Randomly select ten people from each category. b. Each employee has a 4-digit ID number. Randomly choose 40 numbers. c. At the start of each shift, choose every tenth person who arrives for work. d. Randomly select five departments and test all the people who work in those department - doctors, nurses, technicians, clerks, custodians, etc. -Name the sampling strategy in each plan.

Max wants to start a farm to grow mussels. He needs to determine the best environment for growing them. He is going to try two different amounts of salt in the water (salinity) and three different water temperatures. For his experiment he has 18 aquariums, each with 20 mussels. He wants to see which environment produces the largest mussels. -Identify the subjects.

For a school project, Max must design a survey. For his survey he plans to randomly select families and gather information about all the children in each of those families. He must have at least 20 children in his sample. The number of children per family in the U.S. is given in the table below. How many families should Max expect to survey to reach at least 20 children? (treat "5 or more" as 5.) $\begin{array} { | l | l | l | l | l | l | l | } \hline \text { No. of Children } & 0 & 1 & 2 & 3 & 4 & 5 \text { or more } \\\hline \text { \% of families } & 17 & 23 & 25 & 16 & 10 & 9 \\\hline\end{array}$ -State your conclusion.

Double-blinding in experiments is important so that I. The evaluators do not know which treatment group the participants are in. II. The participants do not know which treatment group they are in. III. No one knows which treatment any of the participants is getting.

A researcher wants to compare the effect of a new type of shampoo on hair condition. The Researcher believes that men and women may react to the shampoo differently. Additionally, the Researcher believes that the shampoo will react differently on hair that is dyed. The subjects are Split into four groups: men who dye their hair; men who do not dye their hair; women who dye Their hair; women who do not dye their hair. Subjects in each group are randomly assigned to the New shampoo and the old shampoo. This experiment

UFOs. A National Geographic survey in 2012 found that 36% of Americans believe in aliens. (The outer-space kind, not visitors from foreign countries!) If you were to randomly select 10 Americans, what is the average number of believers you'd expect in your sample? Conduct a simulation to find out! a. Explain how you will use the random numbers listed below to conduct your simulation. b. Carefully label your simulation for 2 trials. c. State your conclusion.

Among a dozen eggs, three are rotten. A cookie recipe calls for two eggs; they'll be selected Randomly from that dozen. Which plan could be used to simulate the number of rotten eggs that Might be chosen? I. Let 0, 1, and 2 represent the rotten eggs, and 3, 4, …, 11 the good eggs. Generate two random Numbers 0-11, ignoring repeats. II. Randomly generate a 0, 1, or 2 to represent the number of rotten eggs you get. III. Since 25% of the eggs are rotten $\text { let } 0 = \text { rotten and } 1,2,3 = \text { good }$ Generate two random numbers 0-3 and see how may 0's you get.

A chemistry professor who teaches a large lecture class surveys his students who attend his class About how he can make the class more interesting, hoping he can get more students to attend. This Survey method suffers from

Administrators at a large hospital are concerned about the possibility of drug abuse by people who work there. They decide to check on the extent of the problem by having a random sample of the employees undergo a drug test. Several plans for choosing the sample are proposed. a. There are four employee classifications: doctors, medical staff (nurses, technicians, etc.) office staff, and support staff (custodians, maintenance, etc.). Randomly select ten people from each category. b. Each employee has a 4-digit ID number. Randomly choose 40 numbers. c. At the start of each shift, choose every tenth person who arrives for work. d. Randomly select five departments and test all the people who work in those department - doctors, nurses, technicians, clerks, custodians, etc. -One administrator suggested walking into the break room and testing the people in there. What type of sampling would this be? Explain why this method is biased. Be sure to name the kind(s) of bias you describe and link it to the variable of interest.

Which statement about bias is true? I. Bias results from random variation and will always be present. II. Bias results from a sampling method likely to produce samples that do not represent the Population. III. Bias is usually reduced when sample size is larger.

A group of people are concerned that the coach of a local high school men's and women's basketball teams alters the amount of air in the basketball to gain an unfair advantage over opponents during home games. The idea is that the basketballs are pumped up with one pound per square inch less air than required, and his teams practiced with these altered balls all week prior to home basketball games. Since these under-pumped basketballs would react differently to being shot at a basket, the team that practiced with these balls would have an unfair advantage when it came to shooting free throws. -Describe how to use a prospective study to determine if the home teams have an unfair advantage when shooting free-throws.

Telephone poll The City Council decides to conduct a telephone poll. Pollsters ask a carefully chosen random sample of adults this question: "Do you favor the construction of a new prison to deal with the high level of violent crime in our State?" In what way might the proportion of "Yes" answers fail to accurately reflect true public opinion? Explain briefly. What kind of bias is this?

Does Procellera Antimicrobial Wound Dressing help injuries heal faster? Researchers checked Records of 38 patients who had been treated for acute or chronic wounds between 2010 and 2012. They found that those who had been treated with Procellera Healed almost twice as fast. This is a

A statistics teacher wants to know how students in her school feel about mathematics courses. She decides to administer a survey to a random sample of students taking a mathematics course. She has several sampling plans to choose from. a. There are four ranks of students taking the class: freshmen, sophomores, juniors, and seniors. Randomly select 15 students from each class rank. b. Randomly select ten math class sections and survey every student in each of those sections. c. Each student has a nine-digit student number. Randomly choose 60 different nine-digit numbers and survey the students that correspond to those numbers. d. Randomly select a number from 1 to 5. Using the class roster, start at that number, then select every fifth student from the list after that. -Name the sampling strategy in each plan.