# Tag Info

## Hot answers tagged ancova

9 votes
Accepted

### How do I understand ANCOVA in basic layman's terms?

To answer your question, I would like to invite you to think of a broader picture for, then, take you back to your original question. First, I would like to introduce a comparison between ANOVA and ...
• 1,483
8 votes

### Between-subjects effect becomes non-signicant after centering covariate. Should I center or not?

Neither, or both, are correct. You often cannot interpret the main effect when you have an interaction in there. The main effect is the difference between the groups when the covariate is equal to ...
• 15.1k
8 votes

### Student's t-test with a covariate?

One common means of controlling for some other covariate would be via regression. Put the X and Y values into the response (DV), and a Y-group indicator (0 if in X, 1 if in Y) as a DV, along with your ...
• 264k
8 votes
Accepted

### Two-way ANOVA vs ANCOVA in R

Order matters whenever the predictors aren't independent. They're correlated in your first example, as they're continuous measurements on each of the diamonds, but not in the second, as those are ...
7 votes

### Difference between two-way ANOVA, factorial ANOVA and ANCOVA: as analogies of linear regression

Compared to one way ANOVA: Two way ANOVA adds one more categorical independent variable to the regression (and possibly the interaction between the two IVs). Factorial ANOVA adds any number of ...
• 95.7k
6 votes
Accepted

### Good data example needed with covariate affected by treatments

You may want to check out the mediation R package. It does include experimental data like jobs and ...
• 1,722
6 votes

### Should covariates that are not statistically significant be 'kept in' when creating a model?

We really need more information about your goals to answer this question. Regressions are used for two main purposes: Prediction Inference Prediction is when your goal is to be able to guess at ...
• 160
6 votes
Accepted

• 4,772
4 votes

### Do I have a justified reason to exclude a non-significant covariate from my ANCOVA? How interesting is unequal variance?

First, ask yourself why IQ is always included in such models. There is probably some reason. It might be that IQ is a mediator (see below) Second, from what you say, it sounds like IQ is a type of ...
• 95.7k
4 votes
Accepted

### Do I have a justified reason to exclude a non-significant covariate from my ANCOVA? How interesting is unequal variance?

First, let me assure you that - as mentioned by @amoeba - you are on the right path to land in "research hell", that is the place where researchers (should) go when they let their p-value to decide ...
• 644
4 votes
Accepted

### Can ANCOVA be used with a dichotomous dependent variable? If not, what have these authors done?

The authors are talking about odds, so I'd guess they used logistic regression with multiple covariables ("multivariable regression"). The terms "ANOVA" and "ANCOVA" do not make much sense in the ...
• 10.9k
4 votes

### Fat tail? Short tail? Long tail? Where do I go from here?

Your Q-Q plot doesn't look like it has a fat tail. I'll show you how a fat tail looks like: Your tail is like a Victoria Secret's model compared to the above. I wish some of my model residuals had ...
• 57.1k
4 votes

### Two-Way ANCOVA: It is necessary to include a non-significant interaction term in the model?

There is nothing in statistical theory or practice which requires you to include any interaction, or any main effect for that matter. You include in your model the variables which your scientific ...
• 16.8k
4 votes

### Two-Way ANCOVA: It is necessary to include a non-significant interaction term in the model?

There are two different definitions or understandings of the term ANCOVA. The first and a broader one is "Any linear model containing continuous/scale predictors besides factors (categorical ...
• 53.3k
4 votes

### Questions concerning visualizing model results with the R-package visreg

The paper by Patrick Breheny and Woodrow Burchett (the authors of visreg) discuss all the issues raised in your question. Before I go into the specific questions, ...
• 26.4k
4 votes
Accepted

### GPower: Difference in Sample Size for ANCOVA vs. Repeated Measures ANOVA in clinical trials

This is a topic for seriously misunderstanding G*Power! Thank you for bringing this up. We thought the following was an explanation for the matter: "When calculating the sample size for "...
4 votes

### ANCOVA vs linear mixed model in R, using different functions gives me different results

To summarise: You've discovered that different packages & functions may implement different methods, so you shouldn't expect to get the same results when you throw your data at a sundry collection ...
• 5,787
3 votes
Accepted

### When to create a control group with paired T test

I think what you are stating is directionally right. But, to clarify you can conduct a paired t test with your one single group and measure how they fare before and after the treatment. You can also ...
• 7,042

Only top scored, non community-wiki answers of a minimum length are eligible