SPSS Assignment

Exercise #1: Independent Samples t-tests (50 points)

A psychologist that specializes in research on religion wants to test the effectiveness of prayer. More specifically, she wondered if prayer would make any difference in the health of medical patients. She selected N=40 participants, half of whom were theists (people who believe in God) and the other half, atheists (people who do not believe in God). The patients were all scheduled to undergo transplant surgery. Starting the day after their surgery, the theist participants were led into prayer every single day while the non-theists patients did not pray.

After 30 days, the health of each patient was then measured on a scale of 1 to 10 using multiple indicators (e.g., complications, blood pressure, red cell count etc.) to see how well they had recovered. Higher scores indicated better recovery and better overall health a month after the surgery.

In variable terms, the researcher would like to know if there are differences in recovery between patients who prayed and those who did not. Is the mean health score different for atheists and theists? The researcher does not believe that there will be a difference.

For this assignment, it is necessary to refer to the accompanying file titled "SPSS Assignment #2 - Independent Samples T-Test data".

"SPSS Assignment #2 - Independent Samples T-Test data".

Patient	Health
1	7.82
1	7.98
1	7.69
1	8.11
1	8.15
1	7.50
1	7.90
1	8.20
1	7.79
1	7.99
1	8.33
1	8.51
1	7.71
1	7.88
1	8.04
1	8.29
1	8.14
1	8.58
1	8.27
1	8.46
2	7.32
2	7.73
2	7.15
2	8.15
2	8.08
2	7.05
2	7.64
2	8.16
2	7.53
2	7.63
2	8.00
2	8.44
2	7.26
2	7.69
2	7.55
2	8.12
2	7.84
2	8.27
2	7.91
2	8.20

Step 1: Setting up your data

1. Input the data into SPSS or Import it using the following steps:

File

Import data

Excel

"Select file"

- Make sure "Read variable names from first row of data", "Percentage of values that determine data type" and "Ignore hidden rows and columns" options are selected

Import

- You may notice that your "engagement" variable has too many zeros. To change that, go to variable view and under decimals, change from 15 to 2.

2. Label and code your data

patients Width: 8

Decimals: 0

Label: Religious orientation of the patient

Values:

1 Atheists

2 Theists

Missing: None

Columns: 8

Align: Center

Measure: Nominal

Role: None

Health Width: 8

Decimals: 2

Label: Overall health of the patient

Values: None

Missing: None

Columns: 10

Align: Center

Measure: Scale

Role: None

Step 2: Answer the following questions using full sentences (18 pts)

a. What are the independent and the dependent variables? (2 pts)

b. What are the scales of measurements of the independent and the dependent variable? (2 pts)

c. State the null and alternative hypotheses? (4pts)

d. Are the hypotheses directional? What kind of test should we use (one-tailed or two-tailed)? (2 pts)

e. Name the three assumptions that must be met for an independent t-test (refer to your textbook pages 310- 316). (2 pts)

- Has the first assumption been met? (2 pts) Why or why not?

f. Conduct normality tests. Copy and paste the results of the table titled Tests of normality (2 pts).

- Based on the results of the Shapiro-Wilks test, has the assumption of normality been met? (2 pts) Why or why not?

Tips: Refer to the video: Normality tests using SPSS

Step 3: Independent Samples T-Test (32 points)

A. Copy and paste the group statistics table and answer the following questions in full sentences, specify mean and standard deviations just like we did in SPSS assignment #1:

a. Which group had better health overall? (4 pts)

b. Which group had greater variability? (4 pts)

B. Copy and paste the Independent Samples Test table and answer the following questions:

Please note: For the next set of questions, answer in full sentences and report statistics via APA. You can report your results using the template below:

"An independent-samples t-test was conducted to compare (your DV) _________ between (IV group / condition 1) ________and (IV group/ condition 2) ________ conditions. There was a significant (or no significant) difference in the scores between IV group 1 (M=___, SD=___) and IV group 2 (M=___, SD=___); t(__)=____, p = ____. The results suggest that [interpret your results using easy-to-understand language]".

For example, if we were reporting data for a study on memory and sugar consumption, we might a sentence would look like this:

"An independent-samples t-test was conducted to compare memory for words in sugar and no sugar conditions. There was a significant difference in the scores for sugar (M=4.2, SD=1.3) and no sugar (M=2.2, SD=0.84) conditions; t(8) = 2.89, p = 0.20. These results suggest that sugar really does have an effect on memory for words. Specifically, our results suggest that when humans consume sugar, their memory for words increases."

a. Has the assumption of homogeneity of variances been met? Why or why not? (2 pts)

b. Report the results of your Independent Samples t-test ( in APA) in one paragraph. Make sure to specify (1) the decision and explain it, (2) what the results means (i.e., was the researcher correct in her prediction? Is there a significant difference between the health of the two groups of patients? If yes, which one? Based on the results was prayer effective?), (3) Write via APA. (18 pts)

Exercise #2: Related-Samples t-tests (50 points)

Surprised by her results on the first study, the same researcher decides to conduct another study focused on assessing the effectiveness of prayer. This time, she wants to avoid any human factor that could emerge as a confounding variable (e.g., placebo effect, discouragement etc.) so she used a sample of 20 bush babies (primates) who were infected with rhodesiense, a parasite that causes fever headaches, confusion, affects muscle coordination and disturbs the sleep cycle. These animals were diagnosed and then prayed for by a group of intercessors for 1 week, after which their symptoms were re-assessed to see if there was any improvement. Consequently, the symptoms of the primates were measured before and after the week of prayer.

The researcher would like to determine whether being prayed for made a difference in the health of the primates. In variable terms, the researcher wants to know if there is a mean difference between the before and after the week of intercession.

For this assignment, refer to the accompanying file titled "SPSS Assignment #2 - Related Samples T-Test data".

Before	After
10.56	10.54
10.09	11.16
10.17	10.31
11.61	11.79
11.79	11.88
9.72	9.81
10.80	10.98
11.79	12.02
10.58	10.76
10.98	11.12
11.64	11.70
12.38	12.38
10.08	10.22
10.76	11.07
11.07	11.35
11.75	11.75
11.25	11.39
12.15	12.24
11.43	11.52
11.93	12.12

Step 1: Setting up your data

1. Input the data into SPSS or import it.

2. Label and code the data

before Width: 8

Decimals: 2

Label: health scores before prayer

Values: None

Missing: None

Columns: 8

Align: Center

Measure: Scale

Role: None

after Width: 8

Decimals: 2

Label: health scores after prayer

Values: None

Missing: None

Columns: 9

Align: Center

Measure: Scale

Role: None

For a repeated or paired-samples t-test, the normality tests are conducted on difference scores, not the values of the paired groups themselves. To accomplish this, First compute the health scores difference and store them in a new variable.

Once that's done then instruct SPSS Statistics to perform the tests of assumptions on this newly created variable, which contains the difference scores. In this example, the new variable that created will be called difference.

Note: There must be a deduct after from before., [before - after].

Step 2: Answer the following questions (18 pts)

a. What are the independent and the dependent variables? (2 pts)

b. What are the scales of measurements of the independent and dependent variables? (2 pts)

c. What are the null and alternative hypotheses? (4 pts)

d. Are the hypotheses directional? What kind of test should we use (one-tailed or two-tailed)? (2 pts)

e. Name the assumptions that must be met for a dependent-samples t-test (refer to your textbook) (2pts).

a. Has the first assumption been met? Why or why not? (2 pts).

b. Conduct tests of normality using the difference variable. Copy and paste the

Shapiro-wilks table (2pts). Has the assumption of normality been met? Why or why not? (2pts).

Tips: to conduct the normality tests with the difference variable, when you get to the 'Explore' tab, simply transfer the difference variable into the dependent list.

Then select plots, 'normality plots with tests', 'continue' and 'ok'.

Step 3: Dependent Samples t-test

A. Copy and paste your paired samples statistics tables and answer the following questions in full sentences, specify mean and standard deviations:

a. Under which condition did the bush babies have the better health on average? (4pts)

b. Which condition had greater variability? (2pts)

c. Effect size (Cohen's d)

You will be required to report effect sizes less often than statistical significance, particularly at the undergraduate level, but they are becoming a more common method of analysis with each passing year and some journals now insist on their inclusion wherever possible. Some SPSS versions provide a measure of effect size with each t-test. You can refer to the table 'Paired Samples Effect sizes. If your SPSS output does not contain effect size, you must calculate it by hand. To calculate an effect size, called d or Cohen's d, for a paired-samples t-test use the formula in your textbook Chapter 11.

- If you computed Compute Cohen's d effect size (1) enter the formula, (2) show your computations (4 pts)

- If you obtained Cohen's d from the Paired Samples Effect Sizes table in your SPSS output, copy and paste the table, The Cohen's d value is located in the 'point estimate' column (4pts).

Then, (3) report your findings (what is the value of Cohen's d) and (4) comment on the magnitude of the effect. Is this a large, small or medium effect size? (2 pts each; 8 pts total for question c).

d. Report the results of your related samples t-test (via APA) in one paragraph. Use the same example as the independent-samples t-test.

Make sure to specify (1) your decision and explain it, (2) what the results means (i.e., was prayer effective? Is there a significant in health before and after prayer? If yes which one?), (3) write up via APA. (18 pts)