Exam 8: Introduction to the T Test: Single Sample and Dependent Means

A research strategy in which each person is tested more than once is known as:

A t test is a hypothesis-testing procedure used when the population variance is unknown. (True or False)

For the following question(s): A school counselor tests the level of depression in fourth graders in a particular class of 20 students. The counselor wants to know whether the kind of students in this class differs from that of fourth graders in general at her school. On the test, a score of 10 indicates severe depression, while a score of 0 indicates no depression. From reports, she is able to find out about past testing. Fourth graders at her school usually score 5 on the scale, but the variation is not known. Her sample of 20 fifth graders has a mean depression score of 4.4. Use the .01 level of significance. -The counselor calculates the unbiased estimate of the population's variance to be 15. What is the variance of the distribution of means?

In a t test for dependent means, 10 participants are each tested twice, making a total of 10 before scores and 10 after scores. What are the degrees of freedom?

What can be said about the "Independence" difference score?

A study tested the effects of science fiction movies on people's belief in the supernatural. A scale was designed to measure the degree that a person believes in the supernatural (high scores indicate high levels of belief). Seven participants completed the scale before and after watching a popular science fiction movie. Participants' scores are listed below. Assume that the researcher had reason to expect participants to believe less in the supernatural after watching the movie. Belief-in-Supernatural Scores, Before and After Watching Science Fiction Movie Carry out a t test for dependent means (using the .01 significance level). a. Use the five steps of hypothesis testing. b. Figure the effect size and find the approximate power of this study.

Power for a t test for dependent means can be determined using:

It is known that a particular laboratory task takes the average person 2.5 seconds. A researcher was interested in whether older people are slower (take longer)on this task. The researcher tested 30 randomly selected 80-year-olds. Their mean time was 2.7 seconds, with an estimated population standard deviation of 1.4 seconds. What should the researcher conclude (use the .05 level)? a. Use the five steps of hypothesis gathering. b. Sketch the distributions involved. c. Explain what you did to a person who is familiar with hypothesis testing with a known population variance and a single sample, including understanding decision errors, effect size, and power, but knows nothing about t tests of any kind.

Which of the following is TRUE about t distributions?

Difference scores are usually used with:

The variance of a sample is said to be "biased" because it consistently __________ the actual variance of the population.

When figuring the variance of the distribution of means based on an estimated population variance in a study with 20 participants, you divide the estimated population variance by __________.

A __________ is a requirement within the logic and mathematics of the t test.

A research article reports results of a study using a t test for dependent means as "t(38)= 3.11, p < .01." This tells you:

The shape of a t distribution:

For the following question(s): A school counselor claims that he has developed a technique to reduce prestudying procrastination in students. He has students time their procrastination for a week and uses this as a pretest (before)indicator of procrastination. Students then attend a workshop in which they are instructed to do a specific warming-up exercise for studying by focusing on a pleasant activity. For the next week, students again time their procrastination. The counselor then uses the time from this week as the posttest (after)measure. -Suppose the counselor found the sum of squared deviations from the mean of the sample to be 135. Given that he tested 10 people, what would be the estimated population variance?

Provide an example of a study that would utilize a t test for a single sample. List three differences in how you would carry out hypothesis testing for a t test for a single sample versus for a Z test.

The t score is your sample's mean minus the __________ divided by the __________.

For the following question(s): A researcher conducts a t test for dependent means in which it is predicted that there will be a decrease in unemployment from before to after a particular job-skills training program. The cutoff t needed is -1.833. The standard deviation of the distribution of means of change scores is 2.0 and the mean change score for the sample studied is an increase of 5.2. -What is the effect size?

Hypothesis testing in which a sample mean is being compared to a known population mean but the population variance is unknown is called a __________.