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Thread: ANOVA or ANCOVA???

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    ANOVA or ANCOVA???




    In a QUASI-EXPERIMENTAL PRE-POST TEST STUDY (factorial design 3x2, instructional method x gender), 6 intact classes were taken & 2 instructors were involved. Out of 6 classes, 2 were randomly assigned to instructional method X, other 2 to method Y & the remaining 2 to method Z. Each instructor was randomly assigned to teach 3 classes by following a different method so as to control teacher differences.

    At pretest stage, it was found that all the 6 sections (comprising 3 different groups) were not significantly different from each other as far as their scores on relevant variables (covariates) was concerned.

    Please suggest: which one is more appropriate to use: ANOVA or ANCOVA?
    (I noticed in a no. of studies that researchers have used ANCOVA preferably in such a case.)

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    Re: ANOVA or ANCOVA???

    Depending on the types of your variables, you might prefer one approach. ANCOVA tries to find the relationship of two continuous variables while adjusting for a categorical variable. In your case, your variables are not continuous. Your response variable seems to be ordinal (but I don't see you have clarified that). If the response variable is continuous, but your independent variables are categorical, ANOVA should be used. Here you have two independent variables: gender and instructional method. Both seem categorical. So I think ANOVA is better.

    Besides, you should check whether ANOVA requirements are met or not. If not, you should consider a non-parametric alternative.

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    statanx (12-19-2012)

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    Re: ANOVA or ANCOVA???

    Quote Originally Posted by victorxstc View Post
    Depending on the types of your variables, you might prefer one approach. ANCOVA tries to find the relationship of two continuous variables while adjusting for a categorical variable. In your case, your variables are not continuous. Your response variable seems to be ordinal (but I don't see you have clarified that). If the response variable is continuous, but your independent variables are categorical, ANOVA should be used. Here you have two independent variables: gender and instructional method. Both seem categorical. So I think ANOVA is better.

    Besides, you should check whether ANOVA requirements are met or not. If not, you should consider a non-parametric alternative.
    Thanks for your reply.
    Dependent variables are three: achievement, attitude towards the teaching subject, attitude towards the instructional method.

    Yeah, data satisfy all the assumptions of ANOVA & even ANCOVA as well.

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    Re: ANOVA or ANCOVA???

    What about ANOVA with repeated measures????????

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    Re: ANOVA or ANCOVA???

    I thought you have determined the type of ANOVA already.

    Repeated-measures ANOVA is fine since you have pre- and post-treatment design. However, if you want to exactly determine the type of the analysis, you need to perform a repeated-measures two-way ANOVA.

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    Re: ANOVA or ANCOVA???


    Quote Originally Posted by victorxstc View Post
    I thought you have determined the type of ANOVA already.

    Repeated-measures ANOVA is fine since you have pre- and post-treatment design. However, if you want to exactly determine the type of the analysis, you need to perform a repeated-measures two-way ANOVA.
    Thanks a lot for your reply.

    Yeah, I determined the type of ANOVA.
    I need to go for 2-way mixed design ANOVA with repeated measures as there are 2 between-subjects factors (Group and Gender) and 1 within-subjects factor (Time: Pre & Post).


    But still I have some problems. I don't know what all assumptions of 2-way mixed design ANOVA with repeated measures I need to test & and how to test them in SPSS & interpret them.

    I know step-wise procedure for ANOVA with repeated measures but not very sure about interpretation & reporting its results in APA style.

    Any suitable link please ............

    One more thing... sample size is 210 (70 in each group).
    Last edited by statanx; 12-20-2012 at 01:09 AM.

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