Mediation & Moderation
A PRIMER, REFRESHER, AND CLARIFICATION OF TERMS
Blimpo & Evans, 2011
“We found that the effect of the WSD program on
learning outcomes is strongly mediated
by the baseline local capacity measured by
adult literacy.”
Blimpo & Evans, 2011
“We found that the effect of the WSD program on
learning outcomes is strongly mediated
by the baseline local capacity measured by
adult literacy.”
Blimpo & Evans, 2011
“We found that the effect of the WSD program on learning outcomes is
strongly mediated by the baseline local capacity measured by adult
literacy.”
*
WSD Program
Receipt
Baseline
Local
Capacity
*
Measured
Student
Learning
Blimpo & Evans, 2011
“We found that the effect of the WSD program on learning outcomes is
strongly mediated by the baseline local capacity measured by adult
literacy.”
wave 1, pre-treatment
implemented between
waves 1 & 2
WSD Program
Receipt
*
Baseline
Local
Capacity
*
Measured
Student
Learning
Blimpo & Evans, 2011
“We found that the effect of the WSD program on learning outcomes is
strongly mediated by the baseline local capacity measured by adult
literacy.”
Baseline
Local
Capacity
WSD Program
Receipt
*
Measured
Student
Learning
Agenda

Moderation

Mediation

Mediated Moderation

Moderated Mediation
CHANGES STRENGTH OF RELATION BETWEEN
TWO VARIABLES
FOR WHOM
MODERATION
UNDER WHAT CONDITIONS
“partitions a focal independent variable
into subgroups that establish its domains of
maximal effectiveness in regard to a given
dependent variable” (Baron & Kenny, 1986)
𝒀𝒊𝒋 = 𝜸𝟎𝟎 + 𝜸𝟎𝟏 𝐌𝐨𝐝 + 𝜸𝟎𝟐 𝐗 + 𝜸𝟎𝟑 𝑴𝒐𝒅𝑿 +𝒖𝟎𝒋 + 𝒓𝒊𝒋
Potential
Moderator
(Mod )
Independent
Variable
(X)
Moderation
𝜸𝟎𝟑
𝜸𝟎𝟐
𝜸𝟎𝟏
Outcome
Variable
(Yi j)
Moderation

Do girls experience a greater increase in confidence than boys after an intensive
math intervention?

Does the program work better or worse in urban areas as compared to rural ones?

Is program impact higher where implementation fidelity was greater?

Does the informational intervention about health prevention operate more
effectively in communities with localized health services?
INTERVENING OR PROCESS VARIABLE
HOW
WHY
MEDIATION
“represents the generative mechanism
through which the focal independent
variable is able to influence the dependent
variable of interest” (Baron & Kenny, 1986)
Indirect effect = ab
a
Independent
Variable
(X)
Mediation
Potential
Mediator
(Med )
c
b
Outcome
Variable
(Yi j)
4 conditions for mediation*
1) The treatment is correlated with the outcome: c path is significant
2) The treatment is correlated with the potential mediator: a path is significant
3) The mediator is correlated with the outcome when controlling for treatment: b
path is significant
4) The effect of the treatment on the outcome is reduced when controlling for the
potential mediator: c’ is zero (full mediation) or non-significant (partial
mediation)
Mediation

Do students experience a greater increase in confidence after an intensive math
intervention because or in accordance with how much their ability improves?

Does the program increase health outcomes through reducing wait time in the local
health clinic?

Does the school intervention increase test scores through changing teachers’
instructional styles?

Do conditional cash transfers impact child health outcomes through increasing
vaccination rates?
Quiz!
A conditional cash transfer to families leads to payment of
school fees which increases children’s enrollment school.
MEDIATOR
MODERATOR
Quiz!
A school-based socioemotional learning program in a conflictaffected countries improves children’s mental health, but not
for children who witnessed prolonged and severe violence.
MEDIATOR
MODERATOR
MEDIATED
MODERATION
What are the mediating
processes through which the
intervention produces differential
effects?
•
Can only happen when the
treatment effect is moderated
•
Different ways for a
moderated treatment effect
to occur
Moderation

Do girls experience a greater increase in confidence than boys after an intensive
math intervention because their ability increases more than boys due to the
intervention?

Does the informational intervention about health prevention operate more
effectively in communities with localized health services because visits to the health
center increase by the most in those communities?
MODERATED
MEDIATION
The mediating process that is
responsible for producing the effect of
the intervention on the outcome
differs as a function of individual
differences or context.
•
Implies identifying a mediating
effect; but does not imply overall
moderation of the treatment effect
•
Different ways for moderated
mediation to occur
Moderated Mediation

On average, all students experience a greater increase in confidence after an
intensive math intervention. Does this operate through increasing actual, measured
aptitude in boys and through increasing perceptions of aptitude in girls?

Do conditional cash transfers impact child health (i.e. mortality) outcomes through
increasing vaccination rates in communities with low baseline vaccination rates and
through increasing nutritional intake in communities with higher baseline vaccination
rates?
Questions?