plot2WayInteraction {petersenlab}

Plot 2-way interaction.

Description

Generates a plot of a 2-way interaction.

Usage

plot2WayInteraction(
  predictor,
  outcome,
  moderator,
  predictorLabel = "predictor",
  outcomeLabel = "outcome",
  moderatorLabel = "moderator",
  varList,
  varTypes,
  values = NA,
  interaction = "normal",
  legendLabels = NA,
  legendLocation = "topright",
  ylim = NA,
  pvalues = TRUE,
  data
)

Arguments

predictor

character name of predictor variable (variable on x-axis).

outcome

character name of outcome variable (variable on y-axis).

moderator

character name of moderator variable (variable on z-axis).

predictorLabel

label on x-axis of plot

outcomeLabel

label on y-axis of plot

moderatorLabel

label on z-axis of plot

varList

names of predictor variables in model

varTypes

types of predictor variables in model; one of:

• "mean" = plots at mean of variable – should be used for ALL covariates (apart from main predictor and moderator)

• "sd" = plots at +/- 1 sd of variable (for most continuous predictors and moderators)

• "binary" = plots at values of 0,1 (for binary predictors and moderators)

• "full" = plots full range of variable (for variables like age when on x-axis)

• "values" = allows plotting moderator at specific values (e.g., 0, 1, 2)

• "factor" = plots moderator at different categories (e.g., TRUE, FALSE)

values

specifies values at which to plot moderator (must specify varType = "values")

interaction

one of:

• "normal" = standard interaction

• "meancenter" = calculates the interaction from a mean-centered predictor and moderator (subtracting each individual's value from the variable mean to set the mean of the variable to zero)

• "orthogonalize" = makes the interaction orthogonal to the predictor and moderator by regressing the interaction on the predictor and outcome and saving the residual

legendLabels

vector of 2 labels for the two levels of the moderator; leave as NA to see the actual levels of the moderator

legendLocation

one of: "topleft", "topright", "bottomleft", or "bottomright"

ylim

vector of min and max values on y-axis (e,g., 0, 10)

pvalues

whether to include p-values of each slope in plot (TRUE or FALSE)

data

name of data object

Details

Generates a plot of a 2-way interaction: the association between a predictor and an outcome at two levels of the moderator.

Value

Plot of two-way interaction.

See Also

Other plot: addText(), ppPlot(), vwReg()

Other multipleRegression: lmCombine(), ppPlot(), update_nested()

Examples

# Prepare Data
predictor <- rnorm(1000, 10, 3)
moderator <- rnorm(1000, 50, 10)
outcome <- (1.7 * predictor) + (1.3 * moderator) +
  (1.5 * predictor * moderator) + rnorm(1000, sd = 3)
covariate <- rnorm(1000)
df <- data.frame(predictor, moderator, outcome, covariate)

# Linear Regression
lmModel <- lm(outcome ~ predictor + moderator + predictor:moderator,
  data = df, na.action = "na.exclude")
summary(lmModel)

# 1. Plot 2-Way Interaction
plot2WayInteraction(predictor = "predictor",
                    outcome = "outcome",
                    moderator = "moderator",
                    varList = c("predictor","moderator","covariate"),
                    varTypes = c("sd","binary","mean"),
                    data = df)

# 2. Specify y-axis Range
plot2WayInteraction(predictor = "predictor",
                    outcome = "outcome",
                    moderator = "moderator",
                    varList = c("predictor","moderator","covariate"),
                    varTypes = c("sd","binary","mean"),
                    ylim = c(10,50),                                  #new
                    data = df)

# 3. Add Variable Labels
plot2WayInteraction(predictor = "predictor",
                    outcome = "outcome",
                    moderator = "moderator",
                    varList = c("predictor","moderator","covariate"),
                    varTypes = c("sd","binary","mean"),
                    ylim = c(10,50),
                    predictorLabel = "Stress",                        #new
                    outcomeLabel = "Aggression",                      #new
                    moderatorLabel = "Gender",                        #new
                    data = df)

# 4. Change Legend Labels
plot2WayInteraction(predictor = "predictor",
                    outcome = "outcome",
                    moderator = "moderator",
                    varList = c("predictor","moderator","covariate"),
                    varTypes = c("sd","binary","mean"),
                    ylim = c(10,50),
                    predictorLabel = "Stress",
                    outcomeLabel = "Aggression",
                    moderatorLabel = "Gender",
                    legendLabels = c("Boys","Girls"),                 #new
                    data = df)

# 5. Move Legend Location
plot2WayInteraction(predictor = "predictor",
                    outcome = "outcome",
                    moderator = "moderator",
                    varList = c("predictor","moderator","covariate"),
                    varTypes = c("sd","binary","mean"),
                    ylim = c(10,50),
                    predictorLabel = "Stress",
                    outcomeLabel = "Aggression",
                    moderatorLabel = "Gender",
                    legendLabels = c("Boys","Girls"),
                    legendLocation = "topleft",                       #new
                    data = df)

#6. Turn Off p-Values
plot2WayInteraction(predictor = "predictor",
                    outcome = "outcome",
                    moderator = "moderator",
                    varList = c("predictor","moderator","covariate"),
                    varTypes = c("sd","binary","mean"),
                    ylim = c(10,50),
                    predictorLabel = "Stress",
                    outcomeLabel = "Aggression",
                    moderatorLabel = "Gender",
                    legendLabels = c("Boys","Girls"),
                    legendLocation = "topleft",
                    pvalues = FALSE,                                  #new
                    data = df)

#7. Get Regression Output from Mean-Centered Predictor and Moderator
plot2WayInteraction(predictor = "predictor",
                    outcome = "outcome",
                    moderator = "moderator",
                    varList = c("predictor","moderator","covariate"),
                    varTypes = c("sd","binary","mean"),
                    ylim = c(10,50),
                    predictorLabel = "Stress",
                    outcomeLabel = "Aggression",
                    moderatorLabel = "Gender",
                    legendLabels = c("Boys","Girls"),
                    legendLocation = "topleft",
                    interaction = "meancenter",                       #new
                    data = df)

#8. Get Regression Output from Orthogonalized Interaction Term
plot2WayInteraction(predictor = "predictor",
                    outcome = "outcome",
                    moderator = "moderator",
                    varList = c("predictor","moderator","covariate"),
                    varTypes = c("sd","binary","mean"),
                    ylim = c(10,50),
                    predictorLabel = "Stress",
                    outcomeLabel = "Aggression",
                    moderatorLabel = "Gender",
                    legendLabels = c("Boys","Girls"),
                    legendLocation = "topleft",
                    interaction = "orthogonalize",                    #new
                    data = df)