Shows how variable interaction shapes change with scaling or a variable having 0 in its range

interactions.R

#preparing data
library(car)
data("Prestige")
df <- Prestige[, c(
  "income",
  "education",
  "prestige"
)]

#making a version of education with its range crossing 0
df$education_0 <- df$education - mean(df$education)

#raw nteraction
df$raw_interaction <- df$education * df$prestige

#raw interaction, 1 crossing 0
df$raw_interaction_0 <- df$education_0 * df$prestige

#interaction of scaled variables
df$interaction_of_scaled <- scale(df$education) * scale(df$prestige)

#interaction of scaled variables, 1 crossing 0
df$interaction_of_scaled_0 <- scale(df$education_0) * scale(df$prestige)

#scaled interaction
df$scaled_interaction <- scale(df$education * df$prestige)

#scaled interaction, 1 crossing 0
df$scaled_interaction_0 <- scale(df$education_0 * df$prestige)

#plotting all that
par(mfrow=c(3, 2))
plot(df$raw_interaction, df$income, main = "interaction of raw variables", xlab = "Interaction", ylab = "Response")
plot(df$raw_interaction_0, df$income, main = "interaction of raw variables (one crosses 0)", xlab = "Interaction", ylab = "Response")
plot(df$interaction_of_scaled, df$income, main = "interaction of scaled variables", xlab = "Interaction", ylab = "Response")
plot(df$interaction_of_scaled_0, df$income, main = "interaction of scaled variables (one crosses 0)", xlab = "Interaction", ylab = "Response")
plot(df$scaled_interaction, df$income, main = "scaled interaction", xlab = "Interaction", ylab = "Response")
plot(df$scaled_interaction_0, df$income, main = "scaled interaction (one crosses 0)", xlab = "Interaction", ylab = "Response")