Spring, 2015

Exam 2

25 points

Please ensure that you have 5 pages. Read each question carefully. Indicate your responses clearly and neatly. If you have a question, please ask me and only me.

__Part 1: Multiple Choice (1 point each)__

__ __

- The shape of the sampling distribution for a single sample t-test is

- a normal bell curve.
- negatively skewed.
- a t-distribution with n-1 degrees of freedom.
- platykurtic.

- If I compute a single sample t-test (two-tailed, α = .05) with a sample size of 15, my critical value will be

- +/- 1.64
- +/- 2.131
- +/- 2.145
- +/- 1.96

- In a single sample experiment, a sample mean is compared to

- alpha.
- a population mean.
- another sample mean.
- the standard error.

- Which of the following is not an assumption of the single sample z-test?

- The dependent variable is interval or ratio.
- The population standard deviation is estimated by
*s*. - The population standard deviation is known.
- The dependent variable scores approximate a normal distribution.

- The values that can vary in a set of data are called the

- degrees of certainty.
- degrees of incarceration.
- degrees of
*n*. - degrees of freedom.

- Suppose you have developed a new six-week smoking cessation program. Several randomly selected smokers follow this program. At the end of the six weeks, you want to find out whether your program was effective in reducing the number of cigarettes smoked in your sample compared to the population. Which of the following tests is most appropriate to use?

- A one-tailed test with the critical value in the upper tail (the positive tail)
- A one-tailed test with the critical value in the lower tail (the negative tail)
- A two tailed test
- Cannot bet determined from the information given

- If I reject the null hypothesis when it is true I have committed

- a Type II error.
- a null error.
- a Type I error.
- no error.

- The region of rejection contains values that

- most likely represent the population.
- represent the null hypothesis.
- represent the most common or typical scores.
- most likely do not represent the population.

- For the single sample z-test, the shape of the sampling distribution for a sample size of 40 will most likely be

- a z-distribution with 39 degrees of freedom.
- a normal distribution.
- platykurtic.
- positively skewed.

- According to the central limit theorem, the mean of the sampling distribution equals

- σ
- µ
*M**n*

__Part 2: Computations__

- A clinical psychologist wants to investigate the effect of a new depression medication. She knows that the mean depression score on the Beck Depression Inventory for her population of clients taking Prozac is µ = 4 (σ = .75) and the scores are normally distributed. She takes a random sample of n = 10 clients and gives them the new drug to see if the sample with the new drug differs from the population in their depression scores. Her sample with the new drug has a mean depression score of
*M*= 2.5 after taking the new drug. Compute the appropriate statistical test to see if there is a difference between the sample and the population. List all six hypothesis testing steps in your answer. Calculate Cohen’s*d*if necessary. In step 6 provide an explanation of your results. 6 points

- A researcher wanted to know if people would spontaneously follow a 24-hour cycle of sleeping and waking if they are not exposed to the usual pattern of sunlight. She believes that her participants will not follow the 24-hour cycle but she doesn’t specify if their cycle will be shorter or longer. To test this, a sample of n = 8 volunteers were individually placed in a room in which there was no light form the outside and no clocks or other indications of time. After one month, the, the mean sleep cycle across the eight participants was
*M*= 24.5 (*s*= 1.20). compute the appropriate statistical test to compare the sample mean to what is assumed to be the average sleep cycle in the general population (µ = 24) to see if the two groups are different. List all of the six hypothesis testing steps in your answer. Calculate Cohen’s*d*if necessary. In step 6 make sure you provide an explanation of your results.

- Suppose a researcher wants to evaluate her clients’ depression scores relative to the general population. In the population the average scores is µ = 12 and σ = 1.5.

- What is the probability of having a depression score above 11 on the scale?

- What is the percentile for a score of 9?

- What is the probability of getting a score below 15?