Report

RStats Statistics and Research Camp 2014 Moderation and Mediation Session 2 Todd Daniel PhD RStats Institute Slide 1 Slide 2 “So far, we have been unable to document any incidents that were sparked by a cellular telephone. In fact, many researchers have tried to ignite fuel vapors with a cell phone and failed.” Petroleum Equipment Institute “The wireless industry has done studies on the potential for wireless phones to create sparks…there is no documented incident where the use of a wireless phone was found to cause a fire or explosion at a gas station.” Federal Communications Commission Slide 3 https://www.youtube.com/watch?v=AIlsJPNMQss Hmmmm… • More gas station fires occur to women • Women are more likely to re-enter the car • Women are less likely to touch the car when exiting • Conclusion: static electricity not cell phones Isn’t this more useful? Slide 4 Stats Tell Us What? Stats tell us what. Grow from whether and if to how and when Slide 5 Next Steps • • • • Slide 6 NHST tells us whether Correlation and Regression tell us if Mediation answers how Moderation answers when Moderation • The combined effect of two variables on another – Conceptually known as moderation – In statistical terms: an interaction effect Moderator Predictor Slide 7 Outcome Example • Do violent video games make teens aggressive? • Participants – 442 youths • IV: Number of hours spent playing video games per week • DV: Aggression • Moderator: Callous (unemotional) traits Slide 8 Conceptual moderation model Callous Traits Game Playing Aggression If callous traits are a moderator then the strength or direction of the relationship between game playing and aggression is affected by callous (unemotional) traits. Slide 9 Treating callous traits as categorical Slide 10 Treating callous traits as continuous Slide 11 The Statistical Moderation Model Predictor Moderator Predictor x Moderator Slide 12 Outcome Centering variables • The interaction term makes the b’s for the main predictors uninterpretable in many situations • For this reason, it is common to transform the predictors using grand mean centering • Centering refers to the process of transforming a variable into deviations around a fixed point Slide 13 Output from moderation analysis Slide 14 Output from moderation analysis II Slide 15 Output from moderation analysis III Slide 16 Following up Moderation with Simple Slopes analysis Slide 17 Simple slopes equations of the regression of aggression on video games at three levels of callous traits Slide 18 Reporting moderation analysis Slide 19 How do I do that? PROCESS www.afhayes.com Plug in for SPSS Slide 20 Mediation Statistical Model Mediation: when the relationship between a predictor variable and outcome variable can be explained by their relationship to a third variable (the mediator) Mediator a b Predictor Slide 21 c' c Outcome Mediated Simple Relationship Relationship Baron & Kenny, (1986) • Mediation is tested through three regression models: 1. Predicting the outcome from the predictor variable 2. Predicting the mediator from the predictor variable 3. Predicting the outcome from both the predictor variable and the mediator Slide 22 Baron & Kenny, (1986) Four conditions of mediation: 1. The predictor must significantly predict the outcome variable. 2. The predictor must significantly predict the mediator. 3. The mediator must significantly predict the outcome variable. 4. The predictor variable must predict the outcome variable less strongly in model 3 than in model 1. Mediator Slide 23 a b Predictor Outcome c' Limitations of Baron & Kenny’s (1986) Approach • How much of a reduction in the relationship between the predictor and outcome is necessary to infer mediation? – people tend to look for a change in significance, which can lead to the ‘all or nothing’ thinking that p-values encourage Slide 24 Sobel Test • An alternative is to estimate the indirect effect and its significance using the Sobel Test (Sobel, 1982) • If the Sobel test is significant, there is significant mediation Slide 25 Effect Sizes of Mediation Kappa-squared (k2) Slide 26 (Preacher & Kelley, 2011) Example of a Mediation Model Indirect Effect a Pornography Consumption Relationship Commitment c' Direct Effect Slide 27 Analysis is conducted in PROCESS b Infidelity Output from Mediation Analysis Slide 28 Output from Mediation Analysis II Slide 29 Output from Mediation Analysis III Slide 30 Output from Mediation Analysis IV Slide 31 Output from Mediation Analysis – Results of Sobel test Slide 32 Reporting Mediation Analysis There was a significant indirect effect of pornography consumption on infidelity though relationship commitment, b = 0.127, BCa CI [0.023, 0.335]. This represents a relatively small effect, κ2 = .041, 95% BCa CI [.008, .104]. Slide 33 Reporting Mediation Analysis Model of pornography consumption as a predictor of infidelity, mediated by relationship commitment. The confidence interval for the indirect effect is a BCa bootstrapped CI based on 1000 samples. Relationship Commitment b = -0.47, p = .028 Pornography Consumption b = -0.27, p < .001 Infidelity Direct Effect, b = 0.46, p = .02 Indirect Effect, b = 0.13, 95% CI [0.02, 0.34] Slide 34 Anything else? • You can do mediation and moderation together • Conditional Process Analysis Slide 35 197 male amateur golfers Stress at Home Self-Efficacy Social Support Slide 36 Rees & Freeman, 2009 Task Performance Rationality of argument Attribution Interaction w/ Outgroup Positive or Negative Slide 37 Popan et al. (2010) Typicality of Outgroup Mbr. Attitude about Outgroup White v. Non-White 172 female freshmen Race Social anxiety Parental Attachment Satisfaction Slide 38 Parade et al. (2010) Satisfaction with Friends Awareness of advertising intent Persuasion Focus Was the advertisement intended to persuade Persuasive Intent Advertising Tactic Brand logos v. Brand logos + slogans Slide 39 Laran, Dalton, and Andrade (2011) Slogan did (not) emphasize saving money Behavioral Prime Willingness to Spend $ $0 to $500 on imaginary shopping spree Take a Break Slide 40 “Static electricity has caused fires at gas stations…for this reason, you should not reenter your vehicle while you are refueling, since static electricity caused by friction from your clothing’s contact with the car seat can ignite the gas when you get back out of the car to complete the refueling process.” Ohio State Bar Association website Slide 41