Foundations of
Psychology Lab 3
Sensation & Perception: T-Test
• https://www.youtube.com/watch?v=0P
d3dc1GcHc (9:56 minutes)
What is a Ttest?
• Goals of a T-test: to determine if the
mean difference is significant and not
due to chance
• Types of T-tests: Independent samples,
Paired samples, One-sample
• P-value: Probability that the difference is
random/due to chance
Null and
Alternative
Hypotheses
• Null Hypothesis
• H0
• States that there is no significant difference
between the groups
• Can be objectively verified, tested, and rejected
• Alternative Hypothesis
• HA
• There is a significant difference between the
groups
https://www.youtube.com/watch?v=ZzeXCKd5a18
(4:28 mins)
Comparing the sample mean to a
proposed population mean
One Sample
T Test
Example
• On average, undergraduate students sleep
for 7 hours on weeknights.
• Research Question: Do Foundations students
get a different amount of sleep on
weeknights than the average?
• Null hypothesis: µFoundationsSleep = 7 hours
• Alternative hypothesis: µFoundationsSleep ≠ 7
SPSS Steps: One
Sample T-Test
Analyze > Compare Means >
One Sample T-Test
Test Variables- Weeknight
Sleep
Test Value- 7 hours (population
average)
Results: One
Sample T-Test
•N= Number of students
•Mean- The average hours slept
in our sample
•Standard Deviation: The SD of
hours slept in our sample
•Standard Error Mean: The
standard error of hours slept in
our sample
Results: One
Sample T-Test
•
•
T = t-score
DF = Degrees of freedom
(N-1)
• Sig = p value for a twotailed test
○ If p < 0.05, reject H0
and accept HA
○ If p > 0.05, retain H0
• Mean Difference = the
sample mean - the test
value
Comparing the means of two
populations
Independent
Samples T
Test
Example
• Students who like Kale will have a different
preference towards running/jogging than
students who do not like Kale
• Independent variable: Kale Preference
(Yes/No)
• Dependent Variable: Running/jogging
Preference (0-100)
• Null hypothesis: µLike Kale = µDo not like kale
• Alternative hypothesis: µLike Kale ≠ µDo not like kale
SPSS Steps:
Independent
Samples T-Test
Analyze > Compare Means >
Independent Samples T-Test
Test Variables- Dependent
Grouping VariableIndependent
Define Groups
SPSS Steps:
Independent
Samples T-Test
Define Groups
(Check in Variable view under
values for the specific numbers)
Group 1: 1 (Yes)
Group 2: 2 (No)
Continue > Ok
Results:
Independent
Samples T-Test
•N= Number of students in each
group
•Mean- The average running
preference for each group
•Standard Deviation: The SD of
running preference for each
group
•Standard Error Mean: The
standard error in running
preference for each group
Results: Independent Samples T-Test
Use the top row (unless Sig under Levene’s Test < 0.05 which is rare)
T= t-score
DF= Degrees of freedom (N1 + N2 -2)
Sig= p value for a two-tailed test
If p < 0.05, reject H0 and accept HA
If p > 0.05, retain H0
Results: Independent Samples T-Test
Conclusion:
• Null hypothesis: µLike Kale = µDo not like kale
• Alternative hypothesis: µLike Kale ≠ µDo not like kale
• T value = 2.342; P value = 0.021
• P value < 0.05, reject the null
APA write up:
The independent samples t test showed that the difference in running preference
between students who do like kale (n = 59 , M = 54.15, SD = 28.39) and the students who do
not like kale (n = 46, M = 41.13, SD = 28.09) is statistically significant, t(103) = 2.34, p = 0.02.
Does Sharing A
Painful
Experience
Increase
Bonding?
• Bastian, Jetten, and Ferris (2014) sought
to examine the effects of shared painful
experiences on cooperation and trust
• Participants were randomly
assigned to either the pain or
control conditions and the
activities were performed in
groups
• Pain Condition
• Completed two tasks designed to
induce pain
• Cold-pressor task
• Hands submerged in ice water for as
long as possible (up to 90 sec)
Pain vs Control
Condition
•
Wall Squat
• Lean against wall with legs at 90 degree
angle
•
Control Condition
•
•
Completed tasks designed to be
purposeful but not painful
E.g. find metal balls at the bottom of
a container
Scales and
Measures Used
• Positive and Negative Affect Scale
• Measure of challenge and threat
response
• A seven-item scale designed to measure
their level of bonding with the other
participants
• Two manipulation checks
• Assessing the intensity and
unpleasantness of the tasks