Question 1

Define t test for independent groups.

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Question 2

How does the variability of the sample data affect the power of the t test? Explain, using the appropriate equations.

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Question 3

You are comparing two methods of psychotherapy, Method A and Method B . You have randomly assigned 10 subjects to method A and 10 other subjects to Method B . The dependent variable is the number of weeks in therapy to achieve a cure. The variance of Method A scores turns out to be somewhat greater than Method B scores. What inference test would you use? Explain.

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Question 4

Define sampling distribution of the difference between sample means.

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Question 5

A professor of women's studies is interested in determining if stress affects the menstrual cycle. Ten women are randomly sampled for an experiment and randomly divided into two groups. One of the groups is subjected to high stress for two months while the other lives in a relatively stress-free environment. The professor measures the menstrual cycle (in days) of each woman during the second month. The following data are obtained.

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Question 6

What are the variables that affect the power of the t test? How does increasing each variable affect power?

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Question 7

Define t test for correlated groups.

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Question 8

A political candidate wishes to determine if endorsing increased social spending is likely to affect her standing in the polls. She has access to data on the popularity of several other candidates who have endorsed increased spending. The data was available both before and after the candidates announced their positions on the issue. The data are as follows: Assuming no other factors were influencing the popularity ratings;

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Question 9

A medical researcher wishes to evaluate the effectiveness of a drug in prolonging the life of a red cell in a culture medium. Seven cultures are treated with saline (an inactive control substance) and seven others are treated with the new drug. The following survival times in days were recorded:

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Question 10

A worker in a neighborhood clinic wishes to assess the impact of showing an educational film on patient compliance in taking an antihypertension medication. The diastolic blood pressure (BP) is used as the dependent variable. During the study the medication dosage was kept constant. Blood pressure was measured one week prior to the film, then the film was shown, and the blood pressure measured again 3 weeks later. The data are shown below:

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Question 11

What are the assumptions underlying the t test for independent groups.

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Question 12

You are interested in whether chewing nicotine gum reduces smoking. You record the number of cigarettes smoked daily by 15 subjects under normal conditions. One week later, you have them chew nicotine gum for two weeks and record the number of cigarettes smoked daily during the two weeks. The data turns out to be very skewed. What inference test would you use? Explain.

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Question 13

A dog food manufacturer believes that he may have found a way to improve the taste of the dog food made by his company. To test the new process, the company recruited 12 dogs. The dogs were given the original food and the time required to eat a standard portion of the food was measured. Two days later the same dogs were fed the same quantity of the new formula and the time was measured again. The following times were recorded: It is assumed that faster eating represents greater preference for the product.

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Question 14

Consider the following data collected from a repeated measures design study.

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Question 15

In addition to determining whether a result is significant, it may be important to know the size of the effect. Is this statement correct? Explain.

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Question 16

Name two inference tests that you have studied for analyzing data from a two condition, correlated groups design. Assuming the data meet the assumption for both tests, which would you use? Why?

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Question 17

Write the number of the symbol shown in Column 1 in the space provided to the left of the term in Column 2 that it represents.

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Question 18

The correlated t test can be considered a special case of the t test for single samples. Is this statement true? Explain.

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Question 19

Five students were tested before and after taking a class to improve their study habits. They were given articles to read which contained a known number of facts in each story. After the story each student listed as many facts as he/she could recall. The following data was recorded.

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Question 20

Compare and contrast the independent groups design with the correlated groups design.

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Quiz 14: Students T Test for Correlated and Independent Groups