Descriptive Statistics

Descriptive Statistics
	N	Minimum	Maximum	Mean	Std. Deviation
total	105	50	125	100.07	14.483
Zscore(total)	105	-3.45694	1.72157	.0000000	1.00000000
Valid N (listwise)	105

Question 1

What is the sample mean (M) and sample standard deviation (s) for total? You will use these values in Question 2 below.

[Answer here in complete sentences. Also insert the output from SPSS here. Replace this prompt and the prompts below, using as much space as necessary to answer questions.]

Question 2

A z score for this sample is calculated as [(X – M) ÷ s]. Locate Case #53’s unstandardized total score (X) in the Data Editor. In the formula below, replace X, M, s, and ? to show how the z score in Ztotal is derived for Case #53.

(X – M ) ÷ s = ?

Question 3

Run Descriptives… on Ztotal. What are the mean and standard deviation of Ztotal? (Hint: “0E7” in SPSS is scientific notation for 0). Are the mean and standard deviation what you would expect? Justify your answer.

[Answer here in complete sentences. Also place the SPSS output here.]

Question 4

Case number 6 has a Ztotal score of 1.51. What does a z value of 1.51 represent?

[Answer here in complete sentences.]

Question 5

Identify the case with the lowest z score. Refer to Appendix A in the Warner (2013) text. Interpret the percentile rank of this z score rounded to whole numbers.

[Answer here in complete sentences.]

Question 6

Identify the case with the highest z score. Refer to Appendix A in the Warner (2013) text. Interpret the percentile rank of this z score rounded to whole numbers.

[Answer here in complete sentences.]

Section 2: Cases Studies of Type I and Type II Errors

Question 7

A jury must determine the guilt of a criminal defendant (not guilty, guilty). Identify how the jury would make a correct decision. Analyze how the jury would commit a Type I error versus a Type II error.

[Answer here in complete sentences.]

Question 8

An I/O psychologist asks employees to complete surveys measuring job satisfaction and organizational citizenship behavior. She intends to measure the strength of association between these two variables. The researcher is concerned that she will commit a Type I error. What research decision influences the magnitude of risk of a Type I error in her study?

[Answer here in complete sentences]

Question 9

A clinical psychologist is studying the efficacy of a new drug medication for depression. The study includes a placebo group (no medication) versus a treatment group (new medication). He then measures the differences in depressive symptoms across the two groups.

What would a Type I error represent within the context of his study? How can he reduce the risk of committing a Type I error? How does this decision affect the risk of committing a Type II error?

[Answer here in complete sentences.]

Section 3: Case Studies of Null Hypothesis Testing

Question 10

You are running a series of statistical tests in SPSS using the standard criterion for rejecting a null hypothesis. You obtain the following p values.

Test 1 calculates group differences with a p value = .07.

Test 2 calculates the strength of association between two variables with a p value = .50.

Test 3 calculates group differences with a p value = .001.

For each test below, state whether or not you reject the null hypothesis. For each test, also explain what your decision implies in terms of group differences (Test 1 and Test 3) and in terms of the strength of association between two variables (Test 2).

Test 1 (group differences) =

Test 2 (strength of association) =

Test 3 (group differences) =

Question 11

A researcher calculates a statistical test and obtains a p value of .86. He decides to reject the null hypothesis. Is this decision correct, or has he committed a Type I or Type II error? Explain your answer.

[Answer here in complete sentences]

Question 12

You are proposing a research study that you would like to conduct while attending Capella University. During the proposal, a committee member asks you to explain in your own words what you meant by saying “p less than .05.” Provide an explanation.

[Answer here in complete sentences]

References

Provide references if necessary. This concludes Unit 4 Assignment 1. Save your answers and upload this template to the assignment area.