Please answer "J-M"
Q1) Independent-Samples
t
Test
(Round calculated results to the hundredth (2
nd
place to the right of the decimal))
In a cognitive psychology experiment, the researcher is interested in whether encoding condition has a significant effect on memory for a set of drawings. In encoding condition A, subjects are asked to name the object in each drawing; in encoding condition B, subjects are asked to name the color of each drawing. Then all subjects are tested on their memory of the drawings. Each recruited subject is randomly assigned to either encoding condition A or encoding condition B.
Based on memory theories, the researcher hypothesized that condition A (object naming) would lead to significantly better memory compared to condition B (color naming), and she sets the significance level at α = .05 for a one-tailed test.
Hint: You may remember a similar scenario in the previous assignment, but with a crucial difference. In the previous assignment, each subject is tested in BOTH condition A and condition B, while each subject here is tested in only ONE condition (either A or B).
Subject ID
|
Encoding A
|
|
Subject ID
|
Encoding B
|
1
|
86
|
|
13
|
90
|
2
|
76
|
|
14
|
85
|
3
|
94
|
|
15
|
81
|
4
|
90
|
|
16
|
76
|
5
|
80
|
|
17
|
73
|
6
|
89
|
|
18
|
83
|
7
|
78
|
|
19
|
79
|
8
|
83
|
|
20
|
75
|
9
|
89
|
|
21
|
87
|
10
|
91
|
|
22
|
88
|
11
|
78
|
|
23
|
84
|
12
|
83
|
|
24
|
86
|
a. What is the dependent (outcome) variable? What is the independent (grouping) variable?
Dependent variable is the score in the memory test of their drawings. Independent variable is the encoding condition with 2 levels A and B.
b. Create the null and alternative hypotheses (directional) for this study, using both words and symbol notation
H0: Mean test score for condition A is equal to the mean test score for condition B.
Ha: Mean test score for condition A is greater/better than condition B.
c. CalculateM
1
and
M
2
(
M1=84.75, M2=82.25
d. Calculatedf1,df2, anddf
total
df1=12-1=11, df2=12-1=11, dfTotal=11+11=22
e. Calculateestimated variance for population 1 (?s12) and estimated variance for population 2 (?s
22)
s12=35.11, s22=30.02
f. Calculate the pooled variance (S
pooled2
)from the two population variances (from question e above)
g. Use the pooled variance (from question f above) to calculate the variance for sampling distribution 1 (S
M12) and the variance for sampling distribution 2 (S
M22)
Hint: Sampling distribution is derived from the original population and it consists of means of all possible samples drawn from the original population.
h. Calculate standard deviation (S
diffmean)of the comparison distribution
Hint: This comparison distribution consists of differences between all possible sample means drawn from the two sampling distributions. Its standard deviation is the denominator of the t statistic formula.
i. Calculate thetstatistic
j. For the one-tailed test, find the critical t values for this hypothesis test based on the total degree of freedom (from question d above), and the preset alpha level.
k. Compare the calculatedtstatistic with the criticaltvalue by stating which is more “extreme”, and then draw a conclusion about the hypothesis test by stating clearly “reject” or “fail to reject” the null hypothesis.
l. Calculate the pooled standard deviation for the populations (use the pooled variance calculated in question f); and then calculate the standardized effect size of this test.
m. Draw a conclusion based on the hypothesis test result and the effect size. In other words, did encoding condition have a significant effect on memory score? Was the effect small, medium, or large?