How to get the percentage concordant and discordant values for a logistic regression model in R?

r
regression
logistic_regression
#1

Hello,

I’ve created a logistic regression model in R using the glm function and then using the summary() function, I got the AIC value, coefficients, signif codes, etc. I want know the values of percentage concordant, tied and discordant for the model. How to get these in R?

Thanks.

#2

Hi Mukesh,

Since R does not have any function to calculate concordance,we need to create one:

concordance<-function(model){
    # Get all actual observations and their fitted values into a frame
      fitted<-data.frame(cbind(model$y,model$fitted.values))
      colnames(fitted)<-c('respvar','score')
      # Subset only ones
      ones<-fitted[fitted[,1]==1,]
      # Subset only zeros
      zeros<-fitted[fitted[,1]==0,]
      
      # Initialise all the values
      pairs_tested<-0
      conc<-0
      disc<-0
      ties<-0
      
      # Get the values in a for-loop
      for(i in 1:nrow(ones))
        {
        for(j in 1:nrow(zeros))
          {
          pairs_tested<-pairs_tested+1
          if(ones[i,2]>zeros[j,2]) {conc<-conc+1}
          else if(ones[i,2]==zeros[j,2]){ties<-ties+1}
          else {disc<-disc+1}
          }
      }
      # Calculate concordance, discordance and ties
      concordance<-conc/pairs_tested
      discordance<-disc/pairs_tested
      ties_perc<-ties/pairs_tested
      return(list("Concordance"=concordance,
                  "Discordance"=discordance,
                  "Tied"=ties_perc,
                  "Pairs"=pairs_tested))
      }

Hope this helps!!

#3

You can compute it using the Concordance() in ‘InformationValue’ package.

Concordance(actuals=ActualsAndScores$Actuals, predictedScores=ActualsAndScores$PredictedScores)