Five hundred students completed the “Census at School” survey. Each was asked ho
ID: 3257855 • Letter: F
Question
Five hundred students completed the “Census at School” survey. Each was asked how many hours per week they spent doing homework. A researcher uses a quasi-experimental design to compare the average time spent doing homework per week to high school students in different grades. The research question is, “Do students in different grades of high school spent significantly different amounts of time doing homework per week?” Five students were randomly selected from each grade; the data is presented below.
What is the effect size?
Use G*Power to estimate the power of the study?
Grade
9
10
11
12
Hours Spent Doing Homework
3
2
1
5
5
2
1
5
2
4
10
4
3
10
2
19
10
12
5
7
Grade
9
10
11
12
Hours Spent Doing Homework
3
2
1
5
5
2
1
5
2
4
10
4
3
10
2
19
10
12
5
7
Explanation / Answer
Answer:
ANOVA
Tests of Between-Subjects Effects
Dependent Variable: time
Source
Type III Sum of Squares
df
Mean Square
F
Sig.
Partial Eta Squared
Noncent. Parameter
Observed Powerb
Corrected Model
193.200a
3
64.400
5.111
.011
.489
15.333
.839
Intercept
627.200
1
627.200
49.778
.000
.757
49.778
1.000
grade
193.200
3
64.400
5.111
.011
.489
15.333
.839
Error
201.600
16
12.600
Total
1022.000
20
Corrected Total
394.800
19
a. R Squared = .489 (Adjusted R Squared = .394)
b. Computed using alpha = .05
Effect size=0.489
F tests - ANOVA: Fixed effects, omnibus, one-way
Analysis: Post hoc: Compute achieved power
Input: Effect size f = 0.489
err prob = 0.05
Total sample size = 20
Number of groups = 4
Output: Noncentrality parameter = 4.7824200
Critical F = 3.2388715
Numerator df = 3
Denominator df = 16
Power (1- err prob) = 0.3392984
power= 0.339
Tests of Between-Subjects Effects
Dependent Variable: time
Source
Type III Sum of Squares
df
Mean Square
F
Sig.
Partial Eta Squared
Noncent. Parameter
Observed Powerb
Corrected Model
193.200a
3
64.400
5.111
.011
.489
15.333
.839
Intercept
627.200
1
627.200
49.778
.000
.757
49.778
1.000
grade
193.200
3
64.400
5.111
.011
.489
15.333
.839
Error
201.600
16
12.600
Total
1022.000
20
Corrected Total
394.800
19
a. R Squared = .489 (Adjusted R Squared = .394)
b. Computed using alpha = .05
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