INTRODUCTION TO ANALYSIS OF VARIANCE (ANOVA - PERSILA

39 Pages·2013·0.54 MB·English

by  Corporate Edition

INTRODUCTION TO ANALYSIS OF
VARIANCE (ANOVA)

24 AUGUST 2013
9:00 am – 1:00 pm
8/24/2013 DR CHEW PPIP USM
The one-way between-subjects ANOVA
• to t est whether the means of three or more
independent groups differ significantly on a dependent

variable of interest

• Data requirements: One independent variable and one
dependent variable
• Independent variable: nominal-scaled variable with
three or more separate groups
• Dependent variable: interval- or ratio-scaled
variable

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Example
• A re searcher wanted to determine whether there was a
significant difference in the number of words correctly

recalled among three different learning strategies

(learning strategies A, B and C)
• 30 students who agreed to participate in the study
were randomly assigned to receive one of the three
strategies (with 10 students in each learning strategy
group)
• After learning the strategy of interest, the students
were shown a list of 15 words for 5 minutes and were
asked to remember as many of the words as possible
using the new strategy
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Example
• Afte r a brief delay, each student wrote down as many
of the words as he or she could remember from the list

• Finally, the researcher recorded the number of words

correctly recalled for each student
• independent variable - learning strategy (three different
learning strategies: A, B and C)
• dependent variable – word recall (the number of words
correctly recalled)

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Null and alternative hypotheses
• Nu ll and alternative hypotheses:
• H : The means of word recall for learning strategy
0
groups A, B and C are equal in the population

• H : At least one of the means is different from the
1
others in the population

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Null and alternative hypotheses
• Wh en the significance level is set at .05, the decision
rule:

• If p ≤ .05, the null hypothesis is rejected. At least one of

the means is different from the others in the population
• Or
• If p > .05, the null hypothesis is not rejected. The
means of word recall for learning strategy groups A, B
and C are equal in the population

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The data
• The d ata for the 30 participants are presented in Table 1.

Table 1

Participant Strategy Number of words
correctly recalled
1 1 8
2 1 10
3 1 9
4 1 7
5 1 9
6 1 7
7 1 10
8 1 8
9 1 12
10 1 9
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The data

Table 1 (continued)

Participant Strategy Number of words

correctly recalled
11 2 12
12 2 10
13 2 9
14 2 10
15 2 9
16 2 8
17 2 12
18 2 10
19 2 10
20 2 12
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The data

Table 1 (continued)

Participant Strategy Number of words
correctly recalled
21 3 6
22 3 4
23 3 5
24 3 6
25 3 4
26 3 2
27 3 5
28 3 3
29 3 7
30 3 5
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Data entry in SPSS v20
• Ste p 1: Create the variables
• 1. S tart SPSS
• 2. C lick Cancel
• 3. Click the Variable View tab
• 4. Click the first cell in the first row and enter the
independent variable name (e.g., strategy)
• 5. Double-click the first cell under the Label column
and enter the independent variable label (learning
strategy)
• 6. Click the first cell under the Values column. An
ellipsis appears in the right-hand corner of the cell.
Click the ellipsis to open the Value Labels dialog box

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