ANCOVA - Using SPSS

ANCOVA - Using SPSS - USING SPSS: ONE-WAY ANALYSIS OF...

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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 one-way 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 Post-Secondary 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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SPSS 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 Post-Secondary 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 homogeneity-of- 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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ANCOVA - Using SPSS - USING SPSS: ONE-WAY ANALYSIS OF...

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