• Formula as follow:
  

where D_m is McIntosh diversity index,N is the total number of individuals in the plant population,

N_i is the number of individuals of the ith species.

• R function as follow:
  

#A R function for calculating the mcIntosh diversity index

mcIntosh<-function(x,MARGIN = 1){

 x <- drop(as.matrix(x))

 if (length(dim(x)) > 1) {

   total <- apply(x, MARGIN, sum)

   Dm<-(total-(rowSums(x^2))^0.5)/(total-total^0.5)

 }

 else {

   Dm <- (sum(x)-(sum(x^2))^0.5)/(sum(x)-sum(x)^0.5)}

 return(Dm)

}

• Example:

  library(vegan)

  data(BCI)

  mcIntosh(BCI)

• mcIntosh.txt