Exam 14: Students T Test for Correlated and Independent Groups

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

The z test for independent groups is seldom used because _________.

A school psychologist is interested in determining if children with attention deficit disorder (ADD) learn better if English literature is read to them rather than having them read the material themselves. A random sample of 10 sixth graders with ADD is selected and divided into two groups of 5 each. One of the groups has a story read to them (Listening Group) and the other reads the story themselves (Reading Group). A quiz on the story is given after each group has finished reading or hearing the story. The following scores were obtained with 20 being a perfect score. What do you conclude, using a = 0.05 2 tail ?

For which of these tests do you need to know the sampling distribution of the relevant statistic in order to use the statistic for hypothesis testing?

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.

can be used to measure the size of effect in conjunction with the single samples t test, the correlated groups t test, and the independent groups t test.

The higher df, the lower t crit becomes for rejecting H₀ .

In the independent groups t test an average of s 12 and s 22 , weighted by the degrees of freedom, is used to estimate s 2 .

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?

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.

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. Assume you are evaluating H ₀ using the t test. The df for determining t crit are _________.

Define homogeneity of variance.

The power of the t test increases with increases in sample variability.

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.

In the independent groups t test, is an estimate of .

Assuming the variability of the scores doesn t change, when using the independent groups t test, the larger the size of effect the larger is .

A health educator wants to evaluate the effect of a dental film on the frequency with which children brush their teeth. A random selection of 8 children are used for the experiment. First, a baseline of the number of times the children brush their teeth over a month's period is established. Next, the children are shown the dental film and again the number of teeth brushings are recorded for a month. The following data are recorded. Assume you are evaluating H 0 with the t test.Using a = .05 2 tail , t crit = _________.

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. The obtained value of the appropriate statistic to evaluate H₀ is _________.

A robust test is relatively insensitive to violations of its underlying mathematical assumptions.

Used in conjunction with the correlated groups t test, gives a value in standard score units for the size of effect.