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U
SING
SPSS:
O
NE

WAY
A
NALYSIS OF
C
OVARIANCE
(ANCOVA)
1.
E
NTERING THE
D
ATA
:
For this example, we are using the HSB500 (High School and Beyond) data file.
Variable names are shown in
bold
, and as such, should be substituted
accordingly to model other examples.
To do a oneway analysis of covariance (ANCOVA) you have to enter the data in
a specific manner. The first column “
subno
” is the subject number assigned to
the student. The second column, “
faed
” is the four levels of the students’ father’s
education, which is our independent variable (1 = Less than High School, 2 =
High School Graduate, 3 = Some Vocational or College, and 4 = College
Graduate or More). The third column contains the students’ standardized
mathematics achievement scores (
mathach
, range 8.333 to 25.000) – the
dependent variable. The fourth column contains the students’
mosaic
score
(range 28.000 to 56.000), which we will use in this example as the covariate.
The summary data (which is generated through the Case Summaries command
in SPSS) for the four groups on both variables,
MATHACH
and
MOSAIC
are
shown below:
Case Summaries
132
132
10.86873
25.29545
6.186632
9.946988
129
129
12.44186
27.18605
6.448802
9.068332
105
105
13.21907
27.00952
6.283149
10.423019
134
134
15.83089
28.07836
6.494654
7.621412
500
500
13.09803
26.88900
6.604590
9.288203
N
Mean
Std. Deviation
N
Mean
Std. Deviation
N
Mean
Std. Deviation
N
Mean
Std. Deviation
N
Mean
Std. Deviation
Father'
s Education Level
Less than High School
High School Graduate
Some PostSecondary Education
College Graduate and Beyond
Total
Mathematics
Test Score
Mosaic
Test Score
Since we have a large sample size (
N
= 500), it is suggested that our
a priori
alpha level be set at .01.
Note
: SPSS will produce a fair amount of output as part of the ANCOVA
statistical process (request), of which only the applicable tables will be shown
and discussed as part of this handout.
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View Full DocumentSPSS STEPS FOR ANCOVA
PAGE 2
Below are the unadjusted means (which are part of the SPSS output generated
from the ANCOVA request) for
MATHACH
for the four groups:
Descriptive Statistics
Dependent Variable: Mathematics Test Score
10.86873
6.186632
132
12.44186
6.448802
129
13.21907
6.283149
105
15.83089
6.494654
134
13.09803
6.604590
500
Father'
s Education Level
Less than High School
High School Graduate
Some PostSecondary Education
College Graduate and Beyond
Total
Mean
Std. Deviation
N
2.
C
ONDUCTING THE
O
NE

WAY
ANCOVA
Before we get started – we must first test the assumptions underlying the
ANCOVA. In addition to testing the assumption of independence and the
assumption of normality we need to conduct a test of the homogeneityof
regression (slopes) assumption. To conduct this test, follow these steps:
1.
Click
Analyze
, click
General Linear Model
, then click
Univariate.
2.
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 Spring '10
 AB
 Covariance, Spss, Variance

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