PSYC 510
HOMEWORK: TWO ROUP ETWEEN UBJECTS ESIGN-G B S D 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 t
test 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 before completing this Learn section 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.
oExample: HW7_JohnDoe_510B01
Make sure to check the before beginning this Homework Grading Rubric 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
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design versus a pretest/posttest control group design? (Must identify at least one advantage
and one disadvantage per design – so four total).
ANSWER
Design Advantages Disadvantages
Posttest-only
1. Simple design and can be done
when pretest is not available or not
possible.
2. Natural response is obtained
without any affect from the pretest
or influence from the experimenter.
1. No comparison group nor a
comparison of the results with any
previous outcome.
2. Requires large sample size, and it is
also less generalizable due to low
external validity.
Pretest/posttest
1. The subjects are usually equal at the
beginning of the study, unless
randomly assigned.
2. There are two measures which can
be compared, and the differences in
the results can be assumed to be the
result of the treatment.
1. The subjects can assume the intent of
the study and may change the
response from the natural / normal
response.
2. In multiple experiments the
experimenter can have influencing
effect on the subjects.
2. What is a confound and how is it related to internal validity?
ANSWER
Confound: A confound is an uncontrolled external / irrelevant variable or omission / error in an
experiment. If a study has been confounded, then it is really hard to say that changes in the dependent
variable were caused by the independent variable or by some uncontrolled extraneous variable.
Relation with Internal Validity: Confound is related to internal validity as a threat to confuse the
results of the study. With respect to the psychological / behavioral studies, confounds interfere due to
human variability, researchers are required to maximize the internal validity by having minimum
differences in the study subjects (given that those are experimental and control groups). A study with
good internal validity is the one having no or minimum confounds. In other words, if there are more
confounds in a given study there will be lesser internal validity showing the lesser / failure of
researcher’s control of the experiment.
3. What is the relationship between external validity and the college sophomore problem?
ANSWER
The college sophomore problem states that most conclusions are reliant on the studies comprising of
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young population who is in late adolescent mentality and still developing their self-identities and
attitudes.
Relation with External Validity: This is an external validity problem due to the “generalization to other
populations” limitation. Generalization to other populations can be problematic as young population is
hardly a representative sample of the population at large, because researchers think that college
sophomores are usually chosen as participants due to their easy and ready availability. And that young
population is prone to self-centeredness, susceptible to social influence, and might change their attitudes,
so their responses might not generalize to other groups.
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
There are two possible problems which have happened in the given scenario:
Regression to the Mean: This phenomenon occurs when volunteers are randomly selected for a study
based on their exceptionally high or extremely low test results. Regression to the mean, which might
occur simply by chance or luck and compromise internal validity, would result in results that were less
extreme and moved closer to the mean if the test were repeated. Meaning that students won't have the
same luck with their scores again.
Testing Effect: The high results received by all students may also be linked to the test's repetition;
students who had previously taken the biology exam would have known what to expect from the
subsequent exam, therefore they had better prepared for it. Due to students' familiarity with and thorough
practice with biology exams, this also poses a danger to internal validity and is known as the "practice
effect."
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
Nonequivalent Control Group: This is a threat to internal validity as the study subjects in control and
experimental groups are not equivalent at the beginning of the study. As the statement speaks itself that
the effectiveness of iron supplements helps women to solve the problems better than those who don’t.
But such groups were made through the self-reporting, researchers compared a group of iron supplement
takers with a group of non-takers both of whom voluntarily participated in the study, hence the groups
are possibly not equivalent. They are not equivalent because some women would have used supplements
to cope up with some disease, so they are different from those who did not have any disease. Some
women would have taken the supplements during pregnancy, some would have taken the supplements on
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doctor’s advice to maintain their health in general, some women would have taken those supplements for
years and some may have just started to use them. So they differ in many ways, they are not same.
Researchers can address this issue through random sampling and random assignment.
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
Independent Variable: Gender –
Nominal Scale
Dependent Variable: Word Searching /
Reading Skill – Ratio Scale
7)
If they reported (25) = 1.80 and it is two-t
tailed, using the critical value table in your
e-book, what is t (do NOT round). Also
cv
state whether the researcher should
REJECT or FAIL TO REJECT the null
hypothesis.
ANSWER
For t(25) = 1.80, df = 25, significance
level or alpha = 0.05:
tcv = +2.0595.
Since t(25) = 1.80 < tcv = 2.0595,
researcher will fail to reject null
hypothesis.
8) Briefly describe a conceptual replication
of this study. Clearly identify how it meets
the definition of a conceptual replication.
ANSWER
Conceptual Replication: This is a
study that is based on another study to
test the same concepts (same in both
studies) but by using different
methods, different manipulation
techniques, or by using different
measures, e.g., researcher may conduct
an observational study in addition to a
true experiment to assess the
generalizability.
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Conceptual Replication of Current
Study: We can select another group of
males and females e.g., working males
and females in age group of 30-40, to
test their spatial / reading skills by
using random sampling and by
providing them different time of
completion, to determine whether the
concept of difference in males’ and
females’ spatial / reading skills is
generalizable and reliable or not.
Fulfilling the Requirement of
Definition: We have changed the
population, we have changed the target
group, we have changed the sampling
method, we have changed the
experiment time, but we are still
replicating the same concept i.e.,
whether there is any difference of
spatial / reading skills of the males and
females?
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
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12 15
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
Group Statistics
Gender N Mean SD SD Error Mean
Spatial_Skills_Word_Recoginition
Male 7 9.8571 1.95180 .73771
Female 7 14.2857 2.56348 .96890
Independent Samples Test
Levene's Test
for Equality of
Variances
t-test for Equality of Means
F Sig. t df Sig. (2-
tailed)
Mean
Difference
Std. Error
Difference
95% Confidence
Interval of the
Difference
Lower Upper
Spatial Skills
Word
Recoginition
Equal
variances
assumed
.550 .473 -3.637 12 .003 -4.42857 1.21778 -7.08189 -1.77525
Equal
variances not
assumed
-3.637 11.207 .004 -4.42857 1.21778 -7.10287 -1.75427
10) Paste appropriate SPSS graph.
ANSWER
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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
R2 = t / t + df
2 2
R2 = (-3.637) / (-3.637) + 12 = 13.23 / 25.23
2 2
R2 = .52
R2 = Large
R2 = 0.1 = small,
R2 = 0.3 = medium
R2 = 0.5 = large
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
An independent samples t-test was run on a random sample of 14 samples of Spatial Skills of
Word Recoginition to determine if there was a mean difference in the Male and Female
groups. There were 7 observarions of Males and 7 of Females, these observations were
randomly assigned to each group. The results showed that Spatial Skills of Word Recoginition
of Males (9.86 + 1.95 words) and Females (14.29 + 2.56 words) had a mean difference (-4.43
words) which was statistically significant (95% CI, -7.08 to -1.78), t(12) = -3.637, p = .003.
So, our null hypothesis was rejected and the Spatial Skills of Word Recoginition Females was
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significantly higher / different than the Males.
13) What is the obtained from your SPSS output? Using your table in the Appendix of t
your e-book, determine the critical value for this study. Clearly identify the t t
obtained and the critical values below. Describe how the critical value can be used tot
determine whether a obtained value will result in a rejection of the null hypothesis t
(i.e. that it is significant).
ANSWER
tobt =
tcv =
tobt = -3.637 (p = .003)
tcv helps in rejection / acceptance of null hypothesis by determining if tobt falls in rejection /
cutoff region or falls outside that region.
tcv = -2.178 (p = .05) – normal significance level – null hypothesis rejected as t is in rejection
obt
region / beyond cutoff value i.e., -2.178 (< -3.637).
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 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.
Self-Regulation Stigma Sensitivity
97 57
67 97
25 89
39 40
80 36
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75 28
45 78
93 45
67 80
85 43
55 75
90 55
14) Paste the appropriate SPSS output to analyze whether sensitivity to higher
prejudice is related to self-regulation ability. lower
ANSWER
Correlations
Self_Regulation Stigma_Sensitivity
Self_Regulation
Pearson Correlation 1 -.470
Sig. (2-tailed) .124
N 12 12
Stigma_Sensitivity
Pearson Correlation -.470 1
Sig. (2-tailed) .124
N 12 12
Above table shows that higher Stigma Sensitivity was not significantly related to lower Self
Regulation (r = -.470, p = .124).
15) Paste an appropriate SPSS graph.
ANSWER
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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
A Pearson correlation coefficient was computed to assess the linear relationship
between Stigma Sensitvity and Self Regulation. There was a negative correlation between the
Stigma Sensitvity and Self Regulation, which was not statistically significant [r(10) = -.470, p
= .124 (two-tailed)]. Since r (.576) was greater than the r value (-.470), therefore null
cv obt
hypothesis was accepted.
Since N = 12, so df = 12 – 2 = 10.
17) If the researcher had made a Type II error, what would the researcher conclude and
what would be the truth?
ANSWER
Type II error (false negative) means null hypothesis was accepted while it was meant to be
rejected. For example, researcher may have concluded that Stigma Sensitvity and Self
Regulation are correlated, while in reality are not correlated with each other. Researcher was
required to reject the null hypothesis instead of accepting it.
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!
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