Experimental Design and Analysis

Part I: General Concepts

Answer the following questions using your own words.

1.

What are some advantages and disadvantages in the use of a posttest-only control group design versus a pretest/posttest control group design? (Must identify at least one advantage and one disadvantage per design – so four total).

ANSWER

2.

What is a confound and how is it related to internal validity?​

ANSWER

3.

What is the relationship between external validity and the college sophomore problem?​

ANSWER

4.

On the most recent exam in your biology class, every student earned an A. The professor claims that he must really be a good teacher for all of the students to have done so well. Given the confounds discussed this week, what alternative explanation can you offer for this result? (Don’t just list a concern– briefly provide a justification).

ANSWER

5.

A health magazine recently reported a study in which researchers claimed that women who take iron supplements have better problem-solving abilities. Further investigation revealed that they assessed problem-solving abilities in a group of women and then had the women self-report whether or not they take iron supplements. Discuss one potential threat to internal validity as it relates specifically to this study.

ANSWER

Scenario: According to some research, males have better spatial skills than do females; and according to other research, females have better reading skills than males. A student is interested in determining which gender performs better on a word-search puzzle (a puzzle in which words are hidden vertically, horizontally, and diagonally within an array of letters) since this type of puzzle involves both spatial and reading skills. A sample of males and females volunteer to participate and are given 10 minutes to work on a 50-word puzzle. The number of words correctly recognized is recorded for each subject. Use this scenario to answer the following questions.

6)

What is the independent variable? Dependent variable? What is the scale of measurement for each?

ANSWER

7)

If they reported t (25) = 1.80 and it is two-tailed, using the critical value table in your e-book, what is tcv (do NOT round). Also state whether the researcher should REJECT or FAIL TO REJECT the null hypothesis.

ANSWER

8)

Briefly describe a conceptual replication of this study. Clearly identify how it meets the definition of a conceptual replication.

ANSWER

Part II: SPSS Application

Research Scenario: According to some research, males have better spatial skills than do females; and according to other research, females have better reading skills than males. A student is interested in determining which gender performs better on a word-search puzzle (a puzzle in which words are hidden vertically, horizontally, and diagonally within an array of letters) since this type of puzzle involves both spatial and reading skills. A sample of males and females volunteer to participate and are given 10 minutes to work on a 50-word puzzle. The number of words correctly recognized is recorded for each subject, and the resulting data are as follows:

Create your SPSS data file to answer the questions below (remember that the IV is your “grouping variable” and will be represented with numbers in SPSS and your DV will be data entered in a second column. Look at the example file from this module’s presentation if you want a visual reminder).

9)

Paste the appropriate SPSS output.

ANSWER

10)

Paste appropriate SPSS graph.

ANSWER

11)

Calculate the r2 effect size given the SPSS output as shown in this module’s presentation. Show all of your work. Interpret it as “small”, “medium” or “large”.

ANSWER

12)

Write an APA-style Results section based on your analyses. Remember to use complete sentences, include the statistical notation, effect size, confidence interval, and include a decision about the null hypothesis. If it is significant, state how by reporting the means and standard deviations.

ANSWER

13)

What is the t obtained from your SPSS output? Using your table in the Appendix of your e-book, determine the critical t value for this study. Clearly identify the t obtained and the t critical values below. Describe how the critical value can be used to determine whether a t obtained value will result in a rejection of the null hypothesis (i.e. that it is significant).

ANSWER

tobt =

tcv =

Part III: Cumulative

Research Scenario: In this fictitious scenario based on a study by Inzlicht and colleagues (2006), researchers examined whether sensitivitiy to race-based prejudice is related to self-regulation abilities in Black college students. They predicted that higher sensitivity to prejudice is related to lower self-regulation ability. Black university students completed two surveys to measure self-regulation abilities and sensitivity to race-based stigma. Both surveys used Likert-based responses; data is provided below for the 12 students. Create an SPSS file to answer the following questions.

14)

Paste the appropriate SPSS output to analyze whether higher sensitivity to prejudice is related to lower self-regulation ability.

ANSWER

15)

Paste an appropriate SPSS graph.

ANSWER

16)

Write an APA-style Results section based on your analyses. Remember to use complete sentences, including the statistical notation following the format provided in the presentations.

ANSWER

17)

If the researcher had made a Type II error, what would the researcher conclude and what would be the truth?

ANSWER

18)

If you were to conduct this study, would you fully disclose the rationale to the participants beforehand? Why or why not? Use the APA Code of Ethics to justify your response (must cite at least one principle and/or code).

ANSWER

Done!