# The moderator–mediator variable distinction in social psychological research: Conceptual, strategic, and statistical considerations.

## Summary (5 min read)

### The Nature o f Moderators

- In general terms, a moderator is a qualitative (e.g., sex, race, class) or quantitative (e.g., level of reward) variable that affects the direction and/or strength of the relation between an independent or predictor variable and a dependent or criterion variable.
- Specifically within a correlational analysis framework, a moderator is a third variable that affects the zero-order correlation between two other variables.
- Such an effect would have occurred in the Stern et al.
- In the dissonanceforced compliance area, for example, it became apparent that the ability of investigators to establish the effects of insufficient justification required the specification of such moderators as commitment, personal responsibility, and free choice (cf. Brehm & Cohen, 1962) .

### Toward Establishing an Analytic Framework for Testing Moderator Effects

- A common framework for capturing both the correlational and the experimental views of a moderator variable is possible by using a path diagram as both a descriptive and an analytic procedure.
- Glass and Singer's (1972) finding of an interaction of the factors stressor intensity (noise level) and controllability (periodic-aperiodic noise), of the form that an adverse impact on task performance occurred only when the onset of the noise was aperiodic or unsignaled, will serve as their substantive example.
- There may also be significant main effects for the predictor and the moderator (Paths a and b), but these are not directly relevant conceptually to testing the moderator hypothesis.
- In addition to these basic considerations, it is desirable that the moderator variable be uncorrelated with both the predictor and the criterion (the dependent variable) to provide a clearly interpretable interaction term.
- Another property of the moderator variable apparent from Figure 1 is that, unlike the mediator-predictor relation (where the predictor is causally antecedent to the mediator), moderators and predictors are at the same level in regard to their role as causal variables antecedent or exogenous to certain criterion effects.

### Choosing an Appropriate Analytic Procedure: Testing Moderation

- In this section the authors consider in detail the specific analysis procedures for appropriately measuring and testing moderational hypotheses.
- Within this framework, moderation implies that the causal relation between two variables changes as a function of the moderator variable.
- The statistical analysis must measure and test the differential effect of the independent variable on the dependent variable as a function of the moderator.
- Tor is a continuous variable and the independent variable is a categorical variable; and in Case 4, both variables are continuous variables.
- To ease their discussion, the authors will assume that all the categorical variables are dichotomies.

### Case 1

- For this case, a dichotomous independent variable's effect on the dependent variable varies as a function of another dichotomy.
- The authors may wish to measure the simple effects of the independent variable across the levels of the moderator (Winer, 1971, pp. 435-436) , but these should be measured only if the moderator and the independent variable interact to cause the dependent variable.

### Case 2

- Here the moderator is a dichotomy and the independent variable is a continuous variable.
- Gender might moderate the effect of intentions on behavior.
- If variances differ across levels of the moderator, then for levels of the moderator with less variance, the correlation of the independent variable with the dependent variable tends to be less than for levels of the moderator with more variance.
- Regression coefficients are not affected by differences in the variances of the independent variable or differences in measurement error in the dependent variable.
- This can be accomplished within the computer program LISREL-VI (J6reskog & S6rbom, 1984) by use of the multiple-group option.

### Case 3

- The indepen- dent variable might be a rational versus fear-arousing attitudechange message and the moderator might be intelligence as measured by an IQ test.
- The fear-arousing message may be more effective for low-IQ subjects, whereas the rational message may be more effective for high-IQ subjects.
- First, the effect of the independent variable on the dependent variable changes linearly with respect to the moderator.
- Unfortunately, theories in social psychology are usually not precise enough to specify the exact point at which the step in the function occurs.
- Alternatively, quadratic moderation can be tested by hierarchical regression procedures described by Cohen and Cohen (1983) .

### Case 4

- In this case both the moderator variable and the independent variable are continuous.
- If one believes that the moderator alters the independent-dependent variable relation in a step function , one can dichotomize the moderator at the point where the step takes place.
- One should consult Cohen and Cohen (1983) and Cleary and Kessler (1982) for assistance in setting up and interpreting these regressions.
- Methods presented by Kenny and Judd (1984) can be used to make adjustments for measurement error in the variables, resulting in proper estimates of interactive effects.
- These methods require that the variables from which the product variable is formed have normal distributions.

### The Nature of Mediator Variables

- Psychologists have long recognized the imporlance of mediating variables.
- Woodworth's (1928) S-O-R model, which recognizes that an active organism intervenes between stimulus and response, is perhaps the most generic formulation of a mediation hypothesis.
- The central idea in this model is that the effects of stimuli on behavior are mediated by various transformation processes internal to the organism.
- Theorists as diverse as Hull, Tolman, and Lewin shared a belief in the importance of postulating entities or processes that intervene between input and output.
- (Skinner's blackbox approach represents the notable exception.).

### General A nalytic Considerations

- In general, a given variable may be said to function as a mediator to the extent that it accounts for the relation between the predictor and the criterion.
- Choice may moderate the impact of incentive on attitude change induced by discrepant action, and this effect is in turn mediated by a dissonance arousal-reduction sequence (of. Brehm & Cohen, 1962) .
- This model assumes a three-variable system such that there are two causal paths feeding into the outcome variable: the direct impact of the independent variable (Path c) and the impact of the mediator (Path b).
- Iftbe residual Path c is not zero, this indicates the operation of multiple mediating factors.

### Testing Mediation

- An ANOVA provides a limited test ofa mediational hypothesis as extensively discussed in Fiske, Kenny, and Taylor (1982) .
- Separate coefficients for each equation should be estimated and tested.
- These three regression equations provide the tests of the linkages of the mediational model.
- Because a successful mediator is caused by the independent variable and causes the dependent variable, successful mediators measured with error are most subject to this overestimation bias.
- Models of this type are estimated by two-stage least squares or a related technique.

### Overview o f Conceptual Distinctions Between Moderators and Mediators

- As shown in the previous section, to demonstrate mediation one must establish strong relations between (a) the predictor and the mediating variable and (b) the mediating variable and some distal endogenous or criterion variable.
- This formulation in no way presupposes that mediators in social psychology are limited to individualistic or "in the head" mechanisms.
- Group-level mediator constructs such as role conflict, norms, groupthink, and cohesiveness have long played a role in social psychology.
- In addition, whereas mediator-oriented research is more interested in the mechanism than in the exogenous variable itself (e.g., dissonance and personal-control mediators have been implicated as explaining an almost unending variety of predictors), moderator research typically has a greater interest in the predictor variable per se.

### Strategic Considerations

- Moderator variables are typically introduced when there is an unexpectedly weak or inconsistent relation between a predictor and a criterion variable (e.g., a relation holds in one setring but not in another, or for one subpopulation but not for another).
- In addition, there may be a wide variation in the strategic functions served by moderators and mediators.
- Therefore, evaluative-anxiety level may be postulated to mediate the differential effectiveness of a given instructional technique.
- Thus, here the authors have a situation where a moderator variable has been useful in suggesting a possible mediator variable.
- Race would be preferred over social class as a moderator if race was more able to tell us something about the processes underlying test performance.

### Operational Implications

- First, the moderator interpretation of the relation between the stressor and control typically entails an experimental manipulation of control as a means of establishing independence between the stressor and control as a feature of the environment separate from the stressor.
- When control is experimentally manipulated in service of a moderator function, one need not measure perceived control, which is the cognitive intraorganismic concept.
- The most essential feature of the hypothesis is that perceived control is the mechanism through which the stressor affects the outcome variable.
- Because of the conceptual status of this assessment in the mediator case, one's main concern is the demonstration of construct validity, a situation that ideally requires multiple independent and converging measurements (Campbell & Fiske, 1959) .
- Thus, when mediation is at issue the authors need to increase both the quality and the quantity of the data.

### A Framework for Combining Mediation and Moderation

- Figure 4 presents a combined model with both mediation and moderation.
- The variable control has both mediator and moderator status in the model.
- It can be explained by P because the control manipulation is differentially affecting perceived control for the levels of the stressor.
- If one wished, further models could be estimated.
- The second-order interaction effect, CPS, could also be estimated and tested.

### I m p l i c a t i o n s and A p p l i c a t i o n s o f the M o d e r a t o r -M e d i a t o r D i s t i n c t i o n

- The authors take the themes developed in the three previous sections and apply them to three areas of social psychological research.
- These areas are personal control, the behaviorintention relation, and linking traits and attitudes to behavior.

### Clarifying the Meaning of Control

- Many investigations of the impact of personal control in social and environmental psychology have been methodologically (but not theoretically) ambivalent with respect to the control variable's causal status.
- This practice leads to serious difficulties of interpretation when a researcher intends to investigate one function of control but studies only the other function.
- Only when this is done can the authors establish the crucial link between perceived control and the criterion.
- Such an interpretation would leave open the possibility that other factors, such as an arousal-labeling or an arousal-amplification mechanism, mediate the effects of density (i.e., Freedman, 1975 , Worchel & Teddlie, 1976) .

### Behavior Intention-Behavior Relation

- Because Fishbein and Ajzen's (1975; Ajzen & Fishbein, 1980) attitude theory of reasoned action is in general highly sophisticated at both the conceptual and quantitative levels, it provides a good example of the extent of confusion regarding mediators and moderators.
- Fishbein and Ajzen assumed that the impact of both attitudes and normative factors on behavior (B) is mediated through behavioral intentions.
- Surprisingly, however, given the elegance of their general model, similar care was not taken regarding the nature of the BI-B link.
- From the present perspective, such an approach ignores the possibility that some of these factors are best conceptualized and treated statistically as moderators whereas others are best viewed as mediators.
- Specifically, Fishbein and Ajzen tested the importance of given factors by looking at the impact on the multiple correla-ti6n of dropping or adding a variable.

### Linking Global Dispositions to Behavior: Attitudes and Traits

- Of all the current areas in social psychology, the one where the use of what the authors have referred to as the combined model is perhaps the strongest is the prediction of social behavior from global dispositional variables.
- What such suggestions lack is precisely the kind of unified conceptual and analytic framework presented in their combined moderator-mediator example .
- Specifically, introducing a moderator variable merely involves a relatively static classification procedure.
- On the other hand, linking the Self-Monitoring Trait relation to a specific mediating mechanism implies that variations in self-monitoring elicit or instigate different patterns of coping or information processing that cause people to become more or less consistent with their attitudes in their behavior.

### S u m m a r y

- First, by carefully elaborating the many ways in which moderators and mediators differ, the authors have tried to make theorists and researchers aware of the importance of not using the terms moderator and mediator interchangeably.
- Received August 7, 1985 Revision received July 14, 1986 9 Instructions to Authors Authors should prepare manuscripts according to the Publication Manual of the American Psychological Association (3rd ed.).
- Each copy of a manuscript to be anonymously reviewed should include a separate title page with authors' names and affiliations, and these should not appear anywhere else on the manuscript.
- Dittoed and mimeographed copies will not be considered.
- Rejection by one section editor is considered rejection by all, therefore a manuscript rejected by one section editor should not be submitted to another.

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##### Citations

25,799 citations

### Cites background or methods from "The moderator–mediator variable dis..."

...For example, the ability to include covariates permits the testing of mediated moderation effects (Baron & Kenny, 1986), in which interaction effects are hypothesized to be mediated; future research might also address how mediated moderation effects may be contrasted in a pairwise manner....

[...]

...By far the most commonly used is the causal steps strategy, popularized by Baron and Kenny (1986), in which the investigator estimates the paths of the model in Figure 1, using OLS regression or SEM, and assesses the extent to which several criteria are met....

[...]

...By far the most commonly used is the causal steps strategy, popularized by Baron and Kenny (1986), in which the investigator estimates the paths of the model in Figure 1, using OLS regression or SEM, and assesses the extent to which several criteria are met. Variable M is a mediator if X significantly accounts for variability in M, X significantly accounts for variability in Y, M significantly accounts for variability in Y when controlling for X, and the effect of X on Y decreases substantially when M is entered simultaneously with X as a predictor of Y. As Kenny, Kashy, and Bolger (1998) note, however, the latter criterion will be satisfied when the first and third criteria are satisfied and when the signs of the effects are consistent with the proposed mediation process....

[...]

15,041 citations

### Cites background or methods from "The moderator–mediator variable dis..."

...After a brief overview of mediation, we argue the importance of directly testing the significance of indirect effects and provide SPSS and SAS macros that facilitate estimation of the indirect effect with a normal theory approach and a bootstrap approach to obtaining confidence intervals, as well as the traditional approach advocated by Baron and Kenny (1986). We hope that this discussion and the macros will enhance the frequency of formal mediation tests in the psychology literature....

[...]

...Rozeboom (1956) coined the term mediation to describe a particular pattern of linear prediction among measured variables, but Judd and Kenny (1981) and Baron and Kenny (1986) are mainly responsible for popularizing mediation models in psychology....

[...]

...Curiously, the Sobel test is discussed, with requisite formulas, by Baron and Kenny (1986), but it is rarely used in practice (cf. MacKinnon et al., 2002)....

[...]

...The Need for a Formal Test Given that Baron and Kenny (1986) provide a conceptually appealing recipe to follow in order to determine the presence or absence of a mediation effect, one may well ask why it is necessary to perform a formal significance test of the indirect effect if the Baron and Kenny criteria have been met. Two broad benefits of formal testing may be suggested. First, there are shortcomings inherent in the Baron and Kenny method. For example, Holmbeck (2002) points out that it is possible to observe a change from a significant XÆY path to a nonsignificant XÆY path upon the addition of a mediator to the model with a very small change in the absolute size of the coefficient. This pattern of results may lead a researcher to erroneously conclude that a mediation effect is present (Type I error). Conversely, it is possible to observe a large change in the XÆY path upon the addition of a mediator to the model without observing an appreciable drop in statistical significance (Type II error). The latter situation is especially likely to occur when large samples are employed because those are the conditions under which even small regression weights may remain statistically significant. Finally, it is possible for a Type I error about mediation to occur if either a or b appears to be statistically different from zero when one of them is in fact zero in the population. A Type I error in the test of either a or b (or both) could lead to an incorrect conclusion about mediation. Second, testing the hypothesis of no difference between the total effect (c) and the direct effect (c¢) more directly addresses the mediation hypothesis than does the series of regression analyses recommended by Baron and Kenny (1986). In the case of simple mediation, the indirect effect of X on Y through M is measured as the product of the XÆM and MÆY paths (ab), which is equivalent to (c c¢) in most situations. Therefore, a significance test associated with ab should address mediation more directly than a series of separate significance tests not directly involving ab. In addition, it has been found that the method described by Baron and Kenny (1986) suffers from low statistical power in most situations (MacKinnon et al....

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...The macros provide unstandardized coefficients for regression Equations 1–3 given above and discussed by Baron and Kenny (1986) as required to test mediation....

[...]

8,940 citations

### Cites background or methods from "The moderator–mediator variable dis..."

...In this article, we focus on the approach to mediation analysis that was articulated by Kenny and his colleagues ( Baron & Kenny, 1986; Judd & Kenny, 1981; Kenny et al., 1998)....

[...]

...14 Collins et al. (1998) and MacKinnon and colleagues (MacKinnon, 2000; MacKinnon et al., 2000) recommended dropping the first step of Baron and Kenny (1986) for a different reason than we do. They considered inconsistent mediating variables that may have effects that go in opposite directions, so the total effect may seem to disappear....

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...The statistical model in this case is technically misspecified because it does not take into account the interaction between group and mediation process ( Baron & Kenny, 1986; described as moderated mediation effects by James & Brett, 1984)....

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... Baron and Kenny (1986) made Equation 2b wellknown, but for large samples Equation 2a is nearly the same magnitude and has been recommended (Mac-Kinnon et al., 1995)....

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... Baron and Kenny (1986) reported that the standard error of the indirect effect estimate can be calculated using a large-sample test provided by Sobel (1982, 1986)....

[...]

8,889 citations

8,629 citations

### Cites background or methods from "The moderator–mediator variable dis..."

...This approach can be traced to the seminal work of Judd and Kenny (1981a, 1981b) and Baron and Kenny (1986) and is the most commonly used approach in the psychological literature....

[...]

...The Baron and Kenny (1986) method had greater power ast8 increased and the Judd and Kenny (1981b) method had less power ast8 increased....

[...]

...…reasons including omitting a variable from the path model, an interaction betweenI and X, incorrect specification of the functional form of the relations, error of measurement in the intervening variable, and a bidirectional causal relation between I and Y (Baron & Kenny, 1986; MacKinnon, 1994)....

[...]

...The most widely used methods proposed by Judd and Kenny (1981b) and Baron and Kenny (1986) have Type I error rates that are too low in all the simulation conditions and have very low power, unless the effect or sample size is large....

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...The majority of the statistical tests of intervening effects reported in psychology journals test the significance of the indirect effectab or each of the causal steps proposed by Judd and Kenny (1981b) or Baron and Kenny (1986)....

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##### References

29,764 citations

26,683 citations

### "The moderator–mediator variable dis..." refers background in this paper

...Because Fishbein and Ajzen's (1975; Ajzen & Fishbein, 1980 ) attitude theory of reasoned action is in general highly sophisticated at both the conceptual and quantitative levels, it provides a good example of the extent of confusion regarding mediators and moderators....

[...]

25,607 citations

15,795 citations

### "The moderator–mediator variable dis..." refers background in this paper

...Because of the conceptual status of this assessment in the mediator case, one's main concern is the demonstration of construct validity, a situation that ideally requires multiple independent and converging measurements (Campbell & Fiske, 1959)....

[...]

...Because of the conceptual status of this assessment in the mediator case, one's main concern is the demonstration of construct validity, a situation that ideally requires multiple independent and converging measurements ( Campbell & Fiske, 1959 )....

[...]

13,453 citations