## STATISTICS: Single-Sample T-Test

PSYC 354

Homework 8

Single-Sample T-Test

When submitting this file, be sure the filename includes your full name, course and section. Example: HW8_JohnDoe_354B01

Be sure you have reviewed this module/week’s lesson and presentations along with the practice data analysis before proceeding to the homework exercises. Complete all analyses in SPSS, then copy and paste your output and graphs into your homework document file. Answer any written questions (such as the text-based questions or the APA Participants section) in the appropriate place within the same file.

Part I: Concepts

Questions 1–3; Answer the questions in the spaces provided.

Part I: Questions 1a-e

Fill in the highlighted blanks with the best word or words.

1-a)

You use a t-test when you know the population ________ but not the population ________.

1-b)

The 2 groups compared in the single-sample t-test are the sample and the ________.

1-c)

The number of scores that are free to vary when you are estimating a population parameter from a sample is called the ________.

1-d)

A researcher reports the results of a single-sample t-test as t(23) = 3.96. The degrees of freedom for this t-test are ______, which means there were ____ total participants in the researcher's sample.

1-e)

Part I: Question 2-3

2)

Explain what each part of the following statistical phrase represents, as it would be reported in APA format: t(19) = 3.15, p = .04

t

19

3.15

P

.04

3)

Calculate the degrees of freedom and identify the critical t value for a single-sample t test in each of the following situations:

3-a) Two-tailed test, N = 9, p = .10

3-b) Two-tailed test, N = 16, p = .05

3-c) One-tailed test, N = 21, p = .01

Part II: SPSS Analysis

Module 8 Exercise File 1

Part II: Questions 1-2

· Open Module 8 Exercise File 1. This file contatins scores on a measure of acute PTSD for 12 children who live in an area recently affected by a natural disaster. Higher scores indicate more acute PTSD symptomology.

· Using these data, run 2 separate single-sample t-tests to compare the sample’s mean acute PTSD score to the following population values:

Population means on PTSD measure for 2 different populations

Population of children in the US: = 12

Population of children in the US who have been victims of abuse :  = 16.2

· For each test, paste the output and write a Results section in current APA style

· As demonstrated in the presentations and in the textbooks.

· There will be 2 sets of output and 2 results sections using this data set

· 1 for each test involving a different population mean.

1-a)

Population of children in the US:  = 12.

Answer: SPSS output of the t-Test

1-b)

Write a results section in current APA style describing the outcome.

All homework results sections must follow the example given in the SPSS presentation. Results sections are paragraphs and must include the APA-formatted statistical statement.

2-a)

Population of children in the US who have been victims of abuse:  = 16.2.

Answer: SPSS output of the t-Test

2-b)

Write a results section in current APA style describing the outcome. See (1b) for details.

Part III: SPSS Data Entry and Analysis

Data provided below.

MMSE Scores

26

24

29

22

23

24

19

28

28

24

29

28

27

25

30

29

26

Part III: Questions 1-2

Do adults at risk of Alzheimer’s disease score differently than the general population of adults on a measure of cognitive functioning? A neuropsychologist assesses the cognitive functioning of 17 adults who are at-risk for Alzheimer’s disease using the Mini-Mental State Examination (MMSE). Higher scores indicate better cognitive functioning. The mean in the general population of healthy adults is 27.5. The data for the participants are shown in the table to the left.

Conduct a single-sample t-test in SPSS to answer the research question.

Create a histogram to display the distribution of the sample.

Write a results section in current APA style.

1-a)

Compute a single-sample t test.

Answer: SPSS output of the t-Test

1-b)

Create a histogram to display the distribution of this sample.

2-a)

Write a results section in current APA style describing the outcome. Refer to earlier directions for details of what is expected.

Part IV: Question 1a & 1b (Non-SPSS)

· Age at onset of dementia was determined in the general population to be  = 68.7 and  = 2.3.

· Use this information to answer the following:

1-a)

Based on the data above, what is the z score for the age of 67?

Work:

1-b)

Using the z table and the z score above, what is the percentile for the age of 67?

Work:

Part IV: Question 2a-2b (Non-SPSS)

For each of the following scenarios, compute the effect size and state whether it is approximately small, medium, or large according to Cohen’s conventions.

2-a)

Participants in an inpatient study of treatment for OCD complete an anxious feelings inventory which is then compared to the general population.

The sample mean is M = 42. The mean in the general population of inpatients on this inventory is  = 39.1, and the population standard deviation is  = 2.7.

Effect Size:

Work:

Small/Med/Large:

2-b)

A mood assessment in a sample of 15 gym members has a mean of M = 18. The mean in the general population on this measure is  = 16.5 with a standard deviation of  = 2.

Effect Size: