Assume that the DV distribution is appropriate for regression

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Assume that the DV distribution is appropriate for regression (unless you are asked to evaluate it).  You do not have to test regression assumptions, except insofar as the questions below specifically ask you to. Data are in Class12_homework_2022.sav.

 

Smith, Fuimaono, and Ioane (2020) collected data from 1000 community-dwelling younger adults. The DV was Dopaminergic Signaling, taken from a continuous measure of dopamine concentration throughout the study visit, assessed via implanted fiber optic cable. Two variables were used to predict dopaminergic signalling:  (1) amount of high-intensity physical activity; and (2) emotion processing speed. Higher levels represent more of the named trait (for processing speed, higher has been coded to mean "faster"). The metric on each of these variables is may be a bit unusual; don’t worry about this, as it represents rescales commonly done in this lab. 

 

1. [__/10] Run the following regression: Dopaminergic signalling = high intensity physical activity + emotion processing speed. Briefly summarize the results. 

 

2. [__/10] It turns out that the dopaminergic signaling DV is a bit platykurtic, and a purist colleague argues that we shouldn’t have run the above regression. As an appeasement step, rerun the regression in #1 as a robust (bootstrapped) regression, winsorizing the DV (20% trimmed mean) and using 1,000 bootstrap samples. Summarize your results; is the pattern of results similar to #1? You do not need to compute standardized betas. Note. As in the in-class assignment, R is not reading the DV as numeric, so you have to fix this before running the winsorization:

 

#Note: For reasons I cannot understand, R does not interpret 

#dopa as a numeric variable.

#To make the winsorization work, you first have to explicitly 

#code dopa as numeric

#See next step. 

 

Wk12$dopa<-as.numeric(Wk12$dopa)

 

#You can then use your psych::winsor statement on dopa

 

 

3. [__/10] Returning to the original (unwinsorized) version of the DV, ignoring the poor distribution, it turns out that high intensity physical activity and emotion processing speed interact. Test the regression: Dopaminergic signalling = high intensity physical activity + emotion processing speed + (high intensity physical activity*emotion processing speed), using mean-centered main effects and Aiken and West mean-centering for the interaction. Please plot the interaction graphically as well. 

 

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