Propensity Score Diagnostics

Checking balance

• Love plots (Standardized Mean Difference)
• ECDF plots

Standardized Mean Difference (SMD)

\[\LARGE d = \frac{\bar{x}_{treatment}-\bar{x}_{control}}{\sqrt{\frac{s^2_{treatment}+s^2_{control}}{2}}}\]

SMD in R

Calculate standardized mean differences

library(halfmoon)
library(tidyverse)

smds <- tidy_smd(
  df,
  .vars = c(confounder_1, confounder_2, ...),
  .group = exposure,
  .wts = wts # weight is optional
)

SMD in R

Plot them! (in a Love plot!)

ggplot(
  data = smds,
  aes(
    x = abs(smd), 
    y = variable, 
    group = method, 
    color = method
  )
) +  
  geom_love()

Love plot