40 votes

What if path c isn't significant, but paths a and b are? Indirect effect in mediation

Your approach to testing mediation appears to conform to the "causal steps approach" described in the classic methods paper by Baron & Kenny (1986). This approach to mediation entails the ...
  • 5,176
13 votes

When is it inappropriate to control for a variable?

I believe the quick one-sentence answer to your question, When is it appropriate to control for variable Y and when not? is the "back-door criterion". Judea Pearl's Structural Causal Model can ...
9 votes
Accepted

Interpreting Mediation Output when Direct Effect is not Stat. Sig but ACME and Total are

This does suggest a "full" mediation, in which all of the IV's influence is mediated. The ACME being significant shows that the mediating process appears to be present. On the other hand, you don't ...
  • 535
8 votes

Alternatives to the Baron-Kenny approach to modeling mediation

Baron and Kenny are indeed outdated, though that does not make them wrong in all cases. The concerns divide into broadly statistical limitations and assumptions which are discussed in the reference ...
8 votes
Accepted

Serial Mediation in R - how to setup the model?

This should probably be migrated to StackOverflow since it is about software, but: You could do this in the R package lavaan. In your model, you would first ...
  • 9,082
7 votes

mediator or moderator variable?

Moderating variables (aka effect modifier, interacting variable, etc.) alter the effect of another variable. In your example increased stress causes decreased well-being, but this effect is altered in ...
  • 27k
7 votes

Alternatives to the Baron-Kenny approach to modeling mediation

This is more a discussion of concerns I have firstly with the approach of Baron and Kenny (which has some bearing on your question), and with a number of more recent papers (I haven't seen them all, ...
  • 264k
7 votes
Accepted

When is it inappropriate to control for a variable?

Conditioning (i.e. adjusting) the probabilities of some outcome given some predictor on third variables is widely practiced, but as you rightly point out, may actually introduce bias into the ...
  • 27k
6 votes
Accepted

R - moderated mediation using the lavaan package

I posted this question in another location and was provided the answer by Terry Jorgenson. Question and answer: I would like to calculate the conditional indirect effects of ...
  • 133
6 votes

Is 'indirect effect' the same as 'mediation'?

No, "mediation" and "indirect effect" are not synonymous. For example, when analyzing complex causal systems in which any variable in the system at time $t$ contributes causally to every variable in ...
  • 27k
6 votes

Testing mediation and moderation; can one variable function as both mediator and moderator?

From definitions, I feel that a variable can not simultaneously function as mediator and moderator. Let's try to investigate both effects: Mediaiton Mediation is a hypothesized causal chain in which ...
  • 1,015
6 votes
Accepted

Causal Mediation Analysis - Negative indirect and total effect, positive direct effect

In mediation analysis, whatever the estimation procedure, it is totally fine to obtain direct and indirect effects with opposite directions. This situation is sometimes referred to as "inconsistent ...
  • 613
5 votes
Accepted

Simulating data for mediation model

The question has been answered by Jake Westfall, but, as I find the question (and the answer) interesting, I decided to develop further. Let say you have the mediation model : $x \rightarrow m \...
  • 463
5 votes
Accepted

Mediation Analysis for Mixed Models

ACME is an acronym for "Average Causal Mediation Effects" ADE is an acronym for "Average Direct Effects" <...
  • 50.7k
5 votes
Accepted

mediation vs interaction - R application

Interaction and mediation are different things. In mediation, we have a causal pathway where one variable causes the mediator and the mediator causes the outcome. In interaction, we have a joint ...
  • 50.7k
4 votes

Alternatives to the Baron-Kenny approach to modeling mediation

Baron and Kenny is distinctly old fashioned these days. They see mediation as a "yes-no" "present-absent" quality; more recent approaches (lots of work by MacKinnon and others) treats it as a ...
  • 95.7k
4 votes
Accepted

Mediation effect size

Report standardized parameter estimates. These are analogous with some sort of effect size. That's what they do in the paper. (You might also ask your supervisor what they actually want - people ...
  • 15.1k
4 votes
Accepted

What is difference between mediation analysis and mendelian randomization analysis?

IV in mediation analysis stands for independent variable not instrumental variable. There is no concept of instruments in mediation analysis. In mediation analysis, the variable of interest is the ...
4 votes

How to do within group moderation analysis without subsetting data

If I'm understanding right, you may be wanting to do an analysis of covariance (ANCOVA). There is a helpful tutorial here (http://r-eco-evo.blogspot.com/2011/08/comparing-two-regression-slopes-by.html)...
  • 96
4 votes
Accepted

In stepwise regression, how to interpret non-significant variables?

If you are interested in interpreting coefficients and significance/p-values, don't use stepwise regression. See this post. In fact, stepwise regression is basically always a bad idea in this day and ...
4 votes
Accepted

Non-significant p-values but CI does not include 0

You should only expect confidence intervals and p-values to align in tests of significance when the same method is used to compute both. In this case, the p-value is computed using a Z-statistic which ...
  • 24.3k
3 votes
Accepted

If x2 & x3 affect x1, & x1 affects y, should x2 & x3 be included in a regression model?

The situation you are referring to is called mediation. Whether you should include $x_2$ and $x_3$ depends on what you want from your model. If you want to test models of complex relationships (e....
3 votes

Can we make mediation analysis with ANOVA?

No, this is not possible. An ANOVA aims to test differences between means of different groups/conditions on one independent variable. E.g. DV: number of strawberries/strawberry plant; IV1: three ...
3 votes

Is 'indirect effect' the same as 'mediation'?

There seem to be two distinct aspects to this question: Are the terms 'indirect effect' and 'mediation' synonymous? I would say largely yes (edit: assuming--cf. @Alexis' answer--that you are ...
3 votes
Accepted

What's an intuitive way to remember the difference between mediation and moderation?

Of course your students should understand the concept, and examples are in order. But a few mnemonics might still be useful. Even though I've done mediation and moderation analyses, I use my mnemonics ...
  • 86
3 votes

Mediation model: is it wrong?

Instability in this context means that it is easier for a single (group of) observation(s) to be influential. So after you have checked for such influential cases (e.g. looking at the dfbetas), ...
  • 19.7k
3 votes
Accepted

Is it allowed to have multiple predictors (not covariates) in causal mediation analysis?

Yes, you could. You may find mediation: R Package for Causal Mediation Analysis written by the authors of the package helpful. Your case is similar to that described in Section 4.2. When doing ...
  • 154
3 votes
Accepted

Are there any circumstances where adjusting for path variables / mediators is useful?

Your intuition is correct, although of course in reality, things are a bit more complex. Suppose you think the causal graph looks like this: Then you can estimate the average causal effect of $D$ on ...
3 votes
Accepted

How should the mediation formulas be applied?

Let's start by computing $\sum_{z}E[y|x', z]p(z|x)$. If $z$ is continuous, you just change the summation to integration, and $p(z|x)$ now refers to the density, $$ \begin{align} \int_z E[y|x', z]p(z|...
3 votes

Mediation analysis: How to interpret an insignificant indirect + insignificant direct effect?

Remember that having p>.05 doesn't mean there is no effect. It means you don't have enough evidence to make a conclusion about the presence or absence of an effect. You do not have enough evidence to ...
  • 24.3k

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