Hi,
I hope this is the right place to post this question.
I have performed a mediation analysis with medeff.
I have an independent variable T, a mediator M, and outcome Y. (All 3 variables are binary, and I use logit)
I first specify the two equations required by medeff.
I make reference to the standard mediation triangle, where path a connects T and M, path b connects M and Y, and path c' connects T and Y.
Equation 1 is simply regressing M on T and some control variables. (this gives and estimate for path a)
Equation 2 regresses Y on M + X +control variables. (this gives estimates for b and c')
What I find is the following:
I get a significant negative association betwee
Equation 1
Equation 2
So, path a is significant and negative, path b is not significant, and path c' is positive and significant.
So, based on that, from what I understand, I would conclude that there is no mediation because path b is not significant.
However, medeff produces the following results:
So, medeff says there is 12% mediation (looking at the last row, % of Total Effect mediated.)
So, my first question is, given the results from the two regression analysis above, should I ignore the medeff results and conclude that there is no mediation?
Or is there actually mediation?
Second question, why if medeff says that there is 12% mediation, would the confidence interval for "average mediation" include 0, ie not significant?
Thank you for any help you can provide.
T Jones
I hope this is the right place to post this question.
I have performed a mediation analysis with medeff.
I have an independent variable T, a mediator M, and outcome Y. (All 3 variables are binary, and I use logit)
I first specify the two equations required by medeff.
I make reference to the standard mediation triangle, where path a connects T and M, path b connects M and Y, and path c' connects T and Y.
Equation 1 is simply regressing M on T and some control variables. (this gives and estimate for path a)
Equation 2 regresses Y on M + X +control variables. (this gives estimates for b and c')
What I find is the following:
I get a significant negative association betwee
Equation 1
M | Coef. Std. | Err. | z P>z [95% | Conf. Interval] | |
T | -3.458955 | .1044635 | -33.11 | 0.000 | -3.6637 -3.25421 |
Y | Coef. | Std. Err. | z | P>z | [95% Conf. | Interval] |
T | .6081007 | .0949606 | 6.40 | 0.000 | .4219813 | .7942201 |
M | -.1496489 | .0989504 | -1.51 | 0.130 | -.3435881 | .0442904 |
So, based on that, from what I understand, I would conclude that there is no mediation because path b is not significant.
However, medeff produces the following results:
Effect Mean | [95% Conf. | Interval] | |
ACME1 | .0189176 | -.005018 | .0438004 |
ACME0 | .0160403 | -.0041128 | .0379756 |
Direct Effect 1 | .1274808 | .0903369 | .1646811 |
Direct Effect 0 | .1246035 | .0863965 | .1633032 |
Total Effect | .1435211 | .1134255 | .1722113 |
% of Total via ACME1 | .1313853 | .1098513 | .1667854 |
% of Total via ACME0 | .1114022 | .0931433 | .141418 |
Average Mediation | .017479 | -.0045654 | .0409513 |
Average Direct Effect | .1260421 | .088528 | .1640466 |
% of Tot Eff mediated | .1213937 | .1014973 | .1541017 |
So, medeff says there is 12% mediation (looking at the last row, % of Total Effect mediated.)
So, my first question is, given the results from the two regression analysis above, should I ignore the medeff results and conclude that there is no mediation?
Or is there actually mediation?
Second question, why if medeff says that there is 12% mediation, would the confidence interval for "average mediation" include 0, ie not significant?
Thank you for any help you can provide.
T Jones
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