[Mediation-information] Prop. Mediated vs. ACME (average).

[Daniel Newman]

Dear mediation gourp,

Firstly, thank you to  Profs. Tingley, Yamamoto, Hirose, Keele, Imai, et
al. for building this R package.  I have just started using it.

I am a little confused about the difference between  "Prop. Mediated
(average)"  and  "ACME (average)". Could anybody help explain this to me?

For example, in the mediate summary below, the 95% CIs show that my "Prop.
Mediated (average)" is significantly greater than zero, but the ACME
(average) is not significantly greater than zero.

Causal Mediation Analysis

Quasi-Bayesian Confidence Intervals

Mediator Groups: AllConds

Outcome Groups: AllConds

Output Based on Overall Averages Across Groups

                         Estimate 95% CI Lower 95% CI Upper p-value
ACME (control)            -0.0684      -0.1537       0.0103     0.1
ACME (treated)            -0.2053      -0.4612       0.0308     0.1
ADE (control)             -3.0298      -6.8686       0.4929     0.1
ADE (treated)             -3.1667      -7.1734       0.5134     0.1
Total Effect              -3.2351      -7.3259       0.5237     0.1
Prop. Mediated (control)   0.0213       0.0139       0.0291     0.0
Prop. Mediated (treated)   0.0640       0.0417       0.0873     0.0
*ACME (average) *           -0.1369      -0.3075       0.0205     0.1
ADE (average)             -3.0983      -7.0210       0.5032     0.1
*Prop. Mediated (average)*   0.0427       0.0278       0.0582     0.0


This output above was generated from the code below - a mediation model to
test whether the continuous mediator ("PrePupilDiameter ") mediates the
relationship between the categorical treatment ("Light") and the continuous
dependent variable ("RT") :

med.fit<-lmer(PrePupilDiameter ~ Light + (1 | AllConds), data =
data_LeftTargets, na.action = na.exclude)
out.fit<-lmer(RT ~ PrePupilDiameter + Light + PrePupilDiameter * Light + (1
| AllConds), data = data_LeftTargets, na.action = na.exclude)
med.out <- mediate(med.fit, out.fit, treat = "Light", mediator =
"PrePupilDiameter",  control.value = 1, treat.value = 3, sims = 100,
outcome="RT")
summary(med.out)

Any help explaining to me the difference between "Prop. Mediated (average)"
 and  "ACME (average)" would be much appreciated

Cheers
Dan
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