#code for Chapter 3 "Propensity Score Weighting" of book:
#Leite, W. L. (2017). Practical propensity score methods using R. 
#Thousand Oaks, CA: Sage. . 
# 
#this is the code that was used to generate the example results in the book
#As the R software and the R packages used in this example are updated frequently
#some incompatibilities between the current code and new R versions or package versions
#may appear
#Any updates to the code will be posted at:
# http://www.practicalpropensityscore.com

#========================================
#EVALUATE COVARIATE BALANCE
  
  
#load data
load(file="Chapter3_ELS_data_imputed_example_career_academy.Rdata")
load(file="Chapter3_ELS_data_imputed_with_weights.Rdata")

#create final weights for the base year
#the final weigth is the product of the propensity score weight
#and the sampling weight
ELS.data.imputed$finalWeightBY <- with(ELS.data.imputed,bystuwt*weightATT)

#evaluate covariate balance for ATT
require(twang)
balanceTable <- bal.stat(ELS.data.imputed, vars= covariateNames,
                        treat.var = "treat", 
                        w.all = ELS.data.imputed$finalWeightBY, get.ks=F,
                        sampw = ELS.data.imputed$bystuwt, 
                        estimand="ATT", multinom=F)
#Table with results of balance evaluation. The columns are:
# tx.mn - The mean of the treatment group
# tx.sd	- The standard deviation of the treatment group
# ct.mn - The mean of the control group
# ct.sd	- The standard deviation of the control group
# std.eff.sz	- The standardized effect size, (tx.mn-ct.mn)/tx.sd. 
# stat	- the t-statistic for numeric variables and the chi-square statistic for categorical variables
# p	- the p-value for the test associated with stat
balanceTable <- balanceTable$results 


#summarize the covariate balance quality
std.eff.sz <- summary(abs(balanceTable$std.eff.sz)) #standardized effect sizes
std.eff.sz

table(abs(balanceTable$std.eff.sz)>0.05)
row.names(balanceTable)[abs(balanceTable$std.eff.sz)>0.05]

#save balance table
write.csv(balanceTable, file="balance_table.csv")