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PSYC 510
HOMEWORK: TWO-GROUP BETWEEN SUBJECTS DESIGN ASSIGNMENT
INSTRUCTIONS
OVERVIEW
This Homework:Two-Group Between Subjects Design Assignment is designed to assess your
understanding of the concepts and applications covered thus far in PSYC 510: Research Methods
and Statistics in Psychology I. Concepts specific to this module include fundamental
considerations for all parametric tests, such as threats to validity, reducing confounding
variables, assumptions for parametric tests. This Homework:Two-Group Between Subjects
Design Assignment also assesses your ability to conduct and interpret the independent samples
ttest using professional conventions. Knowledge from this module will serve as a foundation for
future concepts. These topics also strengthen your ability to critically evaluate whether research
is conducted in a reliable and valid manner in professional and non-professional settings.
INSTRUCTIONS
Be sure you have reviewed this module’s Learn section before completing this
Homework:Two-Group Between Subjects Design Assignment. This Homework:Two-Group
Between Subjects Design Assignment is worth 60 points. Each question is worth 3 points. Six
points are awarded for mechanics/structure.
 Part I contains general concepts from this module’s Learn section.
 Part II requires use of SPSS. You will have to take screen shots and/or copy and paste from
your SPSS to place answers within this file. Make sure you only insert relevant and legible
images.
 Part III is the cumulative section. These may include short answer and/or use of SPSS but
will review material from previous module(s).
 Directions for each subsection are provided in the top of each table (in the blue shaded
areas).
 Answers should be placed where indicated (wherever there is “ANSWER”).
 Submit the file as a WORD document (.doc or .docx). Make sure the filename of your
submission includes your full name, course and section.
o Example: HW7_JohnDoe_510B01
Make sure to check the Homework Grading Rubric before beginning this Homework:Two-
Group Between Subjects Design Assignment.
Part I: General Concepts
These questions are based on the concepts covered in this module’s Learn section.
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).
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The two advantages of using a posttest-only control group design as compared to a pretest/posttest control group
design include the random selection of sample participants which ensures diversity and solid internal validity. The
two disadvantages include the lack of pretest and the high probability of confounds.
The two advantages of using a pretest/posttest control group design include equal grouping of participants before
administering the independent variable and capturing measurements before and after the experiment. The two
disadvantages include reactivity risk and high influence of researcher on the participants.
2. What is a confound and how is it related to internal validity?
A confound refers to a flaw in an experiment and it is associated with the internal validity in a manner that it can
make an experiment seem valid although it is not valid.
3. What is the relationship between external validity and the college sophomore problem?
The relationship between external validity and the college sophomore problem is two dimensional.
Firstly, it does not represent the entire population. Secondly, most of the result is captured from
individuals who are undergoing emotional and intellectual development.
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).
An alternative explanation that can be offered for the result is the testing effect, especially a practice
effect. The most recent test in the biology class could be a repeated one.
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.
One potential threat to the internal validity as it relates specifically to the study is the experimenter or
subject effect. Asking merely whether a woman takes iron supplements could suffice to consciously or
unconsciously affect the outcome.
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
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PSYC 510
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?
The independent variable is gender.
The dependent variables are spatial as well
as reading skills with a scale and nominal
measurement.
7)
If they reported t (25) = 1.80 and it is two-
tailed, using the critical value table in your e-
book, what is t
cv
(do NOT round). Also state
whether the researcher should REJECT or
FAIL TO REJECT the null hypothesis.
t
cv
= 2.064
The researcher should reject the null
hypothesis.
8)
Briefly describe a conceptual replication of
this study. Clearly identify how it meets the
definition of a conceptual replication.
A conceptual replication of the study
could be to offer all participants diverse
tests that test spatial and reading skills
individually.
For testing spatial skills, a Spatial
Visualization Test could be administered
and the participants could read and then
retell a short story. This alternative meets
the definition of a conceptual replication
because the same concepts are being
measured.
Part II: SPSS Application
These questions require the use of SPSS. Remember you must submit all of your work within this
word document. You will need to take a screen shot of your data view if necessary, or copy and
paste your output into the spaces below. Remember to report the exact p value provided by SPSS
output – simply reporting p<.05 or p>.05 is not acceptable (unless SPSS output states p=.000 – in
that case you can report p<.001).
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:
Males Females
12 15
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PSYC 510
8 12
9 11
11 18
10 13
12 14
7 17
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
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PSYC 510
11)
Calculate the r
2
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”.
r
2
= -3.637² / -3.637² - 12 = -13.23 / -25.23 = .52
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.
An independent sample t test was conducted revealing that a statistically significant difference
on the basis of the score of the participants existed:
t(11.207) = -3.637, p = .004, r² = .52, 95% CI (-7.10, -1.75) (two-tailed).
So the null hypothesis was rejected.
As per Figure 1, females scored more than males.
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).
t
obt
= -3.637
t
cv
= -2.179
t
obt
is
inside
the rejection region.
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PSYC 510
Part III: Cumulative
These questions can be related to anything covered thus far in the course.
Research Scenario:In this fictitious scenario based on a study by Inzlicht and colleagues (2006),
researchers examined whether sensitivitiy to race-based prejudiceis 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.
Self-Regulation Stigma Sensitivity
97 57
67 97
25 89
39 40
80 36
75 28
45 78
93 45
67 80
85 43
55 75
90 55
14) Paste the appropriate SPSS output to analyze whether higher sensitivity to prejudice is
related to lower self-regulation ability.
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PSYC 510
15) Paste an appropriate SPSS graph.
16) Write an APA-style Results section based on your analyses. Remember to use complete
sentences, includingthe statistical notation following the format provided in the
presentations.
An independent sample t test was conducted revealing that there existed a statistically significant
difference on the basis of the score of the participants:
t(22) = .847, p = .203, r²=.-.23, 95% CI (-11.46, 27.30) (one-tailed)
So the null hypothesis was rejected.
As per Figure 1, self-regulation scores exceeded that of stigma sensitivity.
17) If the researcher had made a Type II error, what would the researcher conclude and what
would be the truth?
If the researcher had made a Type II error, the researcher would conclude that the sensitivity to prejudice
is associated with lower self-regulation. In reality, sensitivity to prejudice is not related to lower self-
regulation.
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).
I would not fully disclose the rationale to the participants beforehand.
According to Principle C, the integrity of APA Code of Ethics allows certain instances of
deception.
Done!
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