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14 votes
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Difference between Repeated measures ANOVA, ANCOVA and Linear mixed effects model

First there is the question of whether it is OK to use percent change as the outcome. In a regression model with baseline as a regressor this is a very bad idea because the outcome is mathematically ...
Robert Long's user avatar
8 votes
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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 ...
Aaron left Stack Overflow's user avatar
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 ...
Peter Flom's user avatar
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7 votes
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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 "...
Adriaan Hoogendoorn's user avatar
7 votes
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Justifying a smaller control group in survey study

I think you've answered your own question. If your goal is to independently assess the psychometric properties within the control group, collect enough data to do that. If your goal is only to compare ...
Eoin's user avatar
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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 ...
Randy Cragun's user avatar
6 votes
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The lines on my scatterplot for ANCOVA results doesn't look right, personal error or model error?

You appear to be misunderstanding the output from your model. In your code, the line: abline(fit.mice$coefficients[1:2], col="skyblue3") plots a line with the ...
Robert Long's user avatar
6 votes

Why is ANCOVA not appropriate for modelling post-intervention outcome, controlling for baseline

This is explained very clearly in Lüdtke and Robitzsch (2020). I'll briefly summarize their arguments below but the paper is clear and easy to read, and I recommend you read it. Essentially, the ...
Noah's user avatar
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6 votes

ANCOVA with all continuous variables

Instead of ANOVA use regression, which is the more general method: it's perfectly okay to do a regression with any mix of categorical and continuous variables. ANOVA is equivalent to a regression with ...
dipetkov's user avatar
  • 9,560
5 votes

Mixed-effect model / ANCOVA with lmer in R

No, your model is certainly wrong. A continuous variable can't be the grouping factor of a random effect. You need a random effect if the assumption of independence of residuals is violated. Typically ...
Roland's user avatar
  • 6,506
5 votes

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

Growth rates must be distributed as some variation of the Cauchy distribution. I have written a series of papers on this. The Cauchy distribution has no mean so it has no variance or covariance. ...
Dave Harris's user avatar
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5 votes
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Post-Hoc pairwise comparison for slope (interaction term) in R?

If you are using R to do the analysis, the emmeans package has an emtrends function that estimates estimated marginal slopes. e.g., ...
Russ Lenth's user avatar
5 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 ...
ttnphns's user avatar
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5 votes
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Two-Way ANCOVA: It is necessary to include a non-significant interaction term in the model?

It looks like other responses have already addressed the fact that there is no absolute rule that an interaction needs to be included. I'll just echo briefly that the decision of including an ...
Billy's user avatar
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5 votes
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Can this be classified as an ANCOVA?

ANCOVA is terminology that some fields use to mean "linear regression with continuous and categorical variables". If Section is categorical and t is continuous, then I'd say this fits the ...
JTH's user avatar
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4 votes
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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 ...
Michael M's user avatar
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4 votes

Two-way ANOVA vs ANCOVA in R

Stumbled on this question a couple of years after it was posted while looking for some info on ANCOVA with R. Wound up writing a much longer example using the diamonds dataset I won't try and cram it ...
Chuck P's user avatar
  • 206
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 ...
Aksakal's user avatar
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4 votes
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Pairwise comparisons of regression coefficients

Use the emmeans package, specifically pairs(emtrends(m, ~grp, var="var")) ... where grp is ...
Ben Bolker's user avatar
  • 43.1k
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 ...
mdewey's user avatar
  • 17.7k
4 votes

Why is ANCOVA not appropriate for modelling post-intervention outcome, controlling for baseline

DiD vs. ANCOVA has been discussed in my workplace, a health insurance company, where DiD has been the industry standard for some time. I agree that DiD does not adequately account for regression to ...
RobertF's user avatar
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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, ...
COOLSerdash's user avatar
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4 votes
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Different ways to include pre-test performance as a covariate in a linear mixed-effect regression. Which is correct?

A wide variety of interaction terms could be "correct" here, as comments from Robert Long and COOLSerdash suggest. To decide which if any interaction to use involving the ...
EdM's user avatar
  • 90.8k
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 ...
dipetkov's user avatar
  • 9,560
4 votes

ANCOVA in within-subject design

The assumption that age is correlated with cognition is not a statistical assumption, but rather a scientific assumption and there's no need to prove it in a given analysis. It's one thing if the ...
AdamO's user avatar
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3 votes
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ANCOVA interpretation – inconsistency between ANOVA results and pairwise group comparisons

You have been caught in the trap of the difference between anova() and lm() in the ways that they partition variance among the ...
EdM's user avatar
  • 90.8k
3 votes

Best practice when analysing pre-post treatment-control designs

ANCOVA and repeated measures/mixed model for interaction term are testing two different hypothesis. Refer to this article: ariticle 1 and this article: article 2
Thomas's user avatar
  • 81
3 votes

Help with change scores and/or ANCOVA design

For anyone who stumbles upon this question and is interested in determining whether for their type of non-randomized study design, ANCOVA or change scores (or a comparison of both) is more suitable, I ...
Martin S.'s user avatar
3 votes
Accepted

Is this a valid method and does it have a common name? (covariance analysis)

I don't think your analysis is valid. The problem is that when you calculate T2a' and T2b' there is uncertainty in the beta1s and you pretend that those estimates are fixed and correct. Hence your ...
Jeremy Miles's user avatar
  • 17.5k
3 votes

Use of three way Anova or Ancova in R?

The advice you were given - use '+ variable name to indicate that the predictor variable is a covariate - is not correct. + ...
Tim's user avatar
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