Independent Samples T-Test: Placebo Effect and Impulsivity Analysis

This assignment analyzes two datasets using independent samples t-tests to explore the placebo effect and gender differences in impulsivity. The first part examines the effectiveness of two types of placebos (one presented as an active medicine, the other explicitly as a placebo) on neuroticism scores. The analysis includes checking assumptions, interpreting SPSS output, and determining effect size. The second part investigates differences in dysfunctional impulsivity between males and females, including an APA-formatted results section with a figure, statistical test results, and a conclusion relating the findings to the research hypothesis. The student has provided detailed analysis of the statistical tests, including the interpretation of the results, assumptions, and effect sizes. The assignment includes SPSS outputs, and the creation of APA formatted figures. The results show that the Worrigone group did not appear to differ significantly from the Placebo group, while the female group showed significantly higher dysfunctional impulsivity compared to the male group.

Q U E S T I O N 1
1. Task 1
To examine the placebo effect, you jump in the new Heisenberg Time-Machine(TM) and go
back to the 1960s to find a group of 40 patients labelled ‘Neurotic’ by psychiatrists. You
tell 20 of these patients to take a new pill called ‘Worrigone’ three times a day for one
month – but it’s just a sugar pill. The second 20 you tell:
“At the intake conference we discussed your problems and your condition, and it was
decided to consider further the possibility and the need of treatment for you before
we make a final recommendation next month. Meanwhile, we have a month between
now and your next appointment, and we would like to do something to give you
some relief from your symptoms. Many different kinds of tranquilizers and similar
pills have been used for conditions such as yours, and many of them have helped.
Many people with your kind of condition have also been helped by what are
sometimes called "sugar pills," and we feel that a so-called sugar pill may help you,
too. Do you know what a sugar pill is? A sugar pill is a pill with no medicine in it at all.
I think this pill will help you as it has helped so many others. Take this pill three times
a day for the next month."
You measure Neuroticism following treatment using a well-established, valid and reliable
questionnaire. Use an independent t-test test to examine the hypothesis that a placebo
presented as an active medicine is more effective than a placebo explicitly presented as
a placebo. The data can be found in SPSS datafile attached below
(IS_ttest_placebo.sav)
IS_ttest_placebo.sav
Park, L. C., &Covi, U. (1965). An exploration of neurotic patients’
responses to placebo when its inert content is disclosed. Archives
of General Psychiatry, 12, 336-345. Retrieved
from http://www.leecrandallparkmd.net/researchpages/placebo1.ht
ml
__________________________________________________________________________________________
_______________________________
From the data we found that following treatment, Mean Neuroticism scores were (enter
'higher' or 'lower') to a degree for the Worrigone placebo (M = , SD = ) in comparison to
the Sugar Pill placebo (M = , SD = ) group.
The SPSS output is given below
Group Statistics
Placebo type N Mean Std. Deviation Std. Error Mean
Neuroticism Score
Worrigone 20 27.8000 10.59593 2.36932
Sugar Pill 20 27.2500 9.43607 2.10997

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
Neuroticism
Score
Equal variances
assumed
.878 .355 .173 38 .863 .55000 3.17264 -5.87268 6.97268
Equal variances
not assumed
.173 37.500 .863 .55000 3.17264 -5.87549 6.97549
From the data we found that following treatment, Mean Neuroticism scores were higher
to a degree for the Worrigone placebo (M =27.8 , SD = 10.6) in comparison to the Sugar
Pill placebo (M =27.25 , SD = 9.43) group.
10 points
Q U E S T I O N 2
1. Task 1_Q2: Briefly outline the assumptions required for parametric tests such as the
Independent-samples t-test. Does the data from the Placebo experiment (Task 1) appear
to meet such assumptions?
Normality Assumption

Here, we see that the distribution of Neuroticism score has longer tail towards the right side
of the normal curve, indicating that the distribution is skewed right. Thus, the assumption of
normality is not satisfied
Homogeneity of Variances
Levene’s test was used to determine the Homogeneity of Variances assumption. Here, the
value of f test statistic is 0.878 and its corresponding p – value is 0.355 > 0.05, indicating that
the assumption of homogeneity of variances is satisfied
Q U E S T I O N 3
1. Task 1_Q3:
An independent-samples t-test was performed, t =0.173 , p = 0.863, suggesting that the
Worrigone group did not appear to differ significantly from the Placebo group. The effect
size was found to be r =0.052 , which can be considered weak
20 points
Q U E S T I O N 4
1. Task 1_Q4: Create and upload a simpleAPA formatted Figure which best summarises
the data from the Placebo experiment visually (the optimal approach is to convert to
Adobe pdf before uploading!)
From the data we found that following treatment, Mean Neuroticism scores were higher to a
degree for the Worrigone placebo (M =27.8 , SD = 10.6) in comparison to the Sugar Pill
placebo (M =27.25 , SD = 9.43) group. Levene’s test was used to determine the
Homogeneity of Variances assumption. Here, the value of f test statistic is 0.878 and its
corresponding p – value is 0.355 > 0.05, indicating that the assumption of homogeneity of
variances is satisfied. An independent-samples t-test was performed, t =0.173 , p = 0.863,
suggesting that the Worrigone group did not appear to differ significantly from the Placebo
group. The effect size was found to be r =0.052 , which can be considered weak

Q U E S T I O N 5
1. Task 2
Using the Impulsivity data found in IS_Impulse.sav (below), A researcher
was interested in the differences in Impulsivity between the Genders, her
hypothesis was that Males would show greater Dysfunctional Impulsivity
(DI) than Females.
Produce an APA formatted results section summarising the data, providing
an appropriate figure, presenting the results of the appropriate inferential
test (along with effect size) and concluding in plain english how the results
relate to the original hypothesis (again, best to create in word, then
convert and upload in pdf format).
IS_impulse(2).sav
1. Attach File
The SPSS output is given below
Group Statistics
gender N Mean Std. Deviation Std. Error Mean
DI_new
Female 45 30.7111 4.48037 .66789
Male 41 27.9756 4.04653 .63196
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
DI_new
Equal variances
assumed
.690 .409 2.961 84 .004 2.73550 .92389 .89824 4.57276
Equal variances
not assumed
2.975 83.995 .004 2.73550 .91949 .90700 4.56401
From the data we found that following treatment, Mean Dysfunctional Impulsivity were
higher for female respondents (M = 30.71 , SD = 4.48) in comparison to the male respondents

(M =27.98, SD = 4.05) group. Levene’s test was used to determine the Homogeneity of
Variances assumption. Here, the value of f test statistic is 0.690 and its corresponding p –
value is 0.409 > 0.05, indicating that the assumption of homogeneity of variances is satisfied.
An independent-samples t-test was performed, t =2.961, p = 0.005, suggesting that the female
Dysfunctional Impulsivity differ significantly from the male counterparts. The effect size was
found to be r =0.615 , which can be considered moderate. Therefore, there is sufficient
evidence to conclude that Males would show greater Dysfunctional Impulsivity (DI) than
Females