# conceptual difference for conducting ANOVA vs. ANCOVA, and correlation vs. Regression.

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## conceptual difference for conducting ANOVA vs. ANCOVA, and correlation vs. Regression.

 My comment is that in my field, psychology, there is a question about when to use ANOVA vs. ANCOVA. Ostensible, ANOVA tests the differences in means among groups. ANCOVA includes a covariate in this analysis for statistical control. Because when we gather data, we often gather demographic variables along with our predictor and outcome variables. If the hypothesis is to test the difference among means among three groups, and the selected analysis is ANOVA, the question is raised, why not use an ANCOVA and include the covariates for statistical control? If that is the case, then that would make every analysis where the intent is to compare group means, an ANCOVA because why wouldn't you want to include covariates for statistical control? Granted including the covariates means giving up statistical power, but conserving statistical power shouldn't be the reason for using an ANOVA versus an ANCOVA. In other words, assuming a sufficient sample size, why not conduct an ANCOVA every time instead of an ANOVA if you have covariates, especially demographics, where you can enter the covariates for statistical control? That would mean we would conduct ANCOVA’s every chance we get, i.e., whenever we have covariates. I would rather have the decision to use ANOVA vs. ANCOVA be based on conceptual and/or statistical grounds, but I can't seem to find such a justification for using ANOVA vs. ANCOVA. Thanks for your comments, and any articles or website references are appreciated.   Another comment is that among my peers, they tend to think that a regression, rather than correlations, should always be conducted whenever you have several continuous variables. The idea is that if you have several predictor variables, why not throw them all together and see which ones have the stronger associations with the outcome variable? It is often, if not always the case, that we are collecting data on several predictor variables and one outcome variable. Once my colleagues see a correlation matrix, they are quick to point out, why not just a regression with all of the independent variables and see what happens?  It’s as if my colleagues think of a regression as a “sophisticated” analysis compared to simple correlations. If I follow my colleagues logic, then why not run a regression every time you have multiple independent variables, and why bother with correlations? I maintain that you shouldn’t use a regression “just to see what happens”; you need a conceptual reason for wanting to examine the independent variables simultaneously.  My question is, what is the conceptual difference or rationale for conducting correlations among variables, rather than just using regression? Thanks for your comments, and any articles or website references are appreciated.   Peter Ji Adler University ===================== To manage your subscription to SPSSX-L, send a message to [hidden email] (not to SPSSX-L), with no body text except the command. To leave the list, send the command SIGNOFF SPSSX-L For a list of commands to manage subscriptions, send the command INFO REFCARD
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## Re: conceptual difference for conducting ANOVA vs. ANCOVA, and correlation vs. Regression.

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## Re: conceptual difference for conducting ANOVA vs. ANCOVA, and correlation vs. Regression.

 In reply to this post by pji >>>Granted including the covariates means giving up statistical power, but conserving statistical power shouldn't be the reason for using an ANOVA versus an ANCOVA. In other words, assuming a sufficient sample size, why not conduct an ANCOVA every time instead of an ANOVA if you have covariates, especially demographics, where you can enter the covariates for statistical control?<<<<< When you include covariates, you actually gain power for your focal prediction as you are removing noise from it, if my understanding is correct per Cohen's exposition of just this case. This is the case of f2. -- Sent from: http://spssx-discussion.1045642.n5.nabble.com/===================== To manage your subscription to SPSSX-L, send a message to [hidden email] (not to SPSSX-L), with no body text except the command. To leave the list, send the command SIGNOFF SPSSX-L For a list of commands to manage subscriptions, send the command INFO REFCARD