Measuring Agreement in R: An Introduction

Agreement is a fundamental concept for many research fields, including medical, psychological, and educational research. When conducting studies that involve multiple raters or observers, it is critical to have a way to measure the level of agreement between them. One way to measure agreement is by using statistical tools such as Cohen’s kappa, Kendall’s tau, or Intraclass Correlation Coefficients (ICC).

R is a powerful statistical software that provides various functions to measure agreement. In this article, we will discuss some popular functions in R that can be used to estimate agreement in research data.

Cohen’s Kappa

Cohen’s Kappa is a widely used statistic to measure the level of agreement between two raters. It measures the agreement beyond chance, and its scores range from -1 to 1. A kappa value of 0 indicates no agreement, while 1 indicates perfect agreement.

In R, the “kappa2” function from the “irr” package can be used to calculate Cohen’s kappa. The function takes two vectors as inputs, where each vector represents the ratings of each rater. Here is an example code:

library(irr)

rater1 <- c(1, 2, 3, 4, 5)

rater2 <- c(1, 2, 4, 4, 5)

kappa2(rater1, rater2)

The output will be a kappa value that indicates the level of agreement between the two raters.

Kendall’s Tau

Kendall’s Tau is another popular statistic used to measure concordance or agreement between two raters. It is a non-parametric statistic that measures the degree of association between two variables. The values of Kendall`s tau range from -1 to 1, where -1 represents perfect disagreement, 0 represents no relationship, and 1 represents perfect agreement.

In R, the “cor.test” function can be used to calculate Kendall’s tau. Here is an example code:

rater1 <- c(1, 2, 3, 4, 5)

rater2 <- c(1, 2, 4, 4, 5)

cor.test(rater1, rater2, method = “kendall”)

The output will show the value of Kendall’s tau and the p-value.

Intraclass Correlation Coefficients (ICC)

Intraclass Correlation coefficients (ICC) are used to measure inter-rater reliability or agreement between multiple raters. It is a statistical method that estimates the proportion of variance that is due to the category of raters. ICC values range from 0 to 1, where 0 indicates no agreement and 1 indicates perfect agreement.

In R, the “ICC” function from the “irr” package can be used to calculate ICC. The function takes a matrix as its input, where each row represents a rater and each column represents the item being rated. Here is an example code:

library(irr)

ratings <- matrix(c(1, 2, 3, 4, 5,

1, 2, 4, 4, 5,

2, 3, 4, 4, 5),

nrow = 3, ncol = 5, byrow = TRUE)

ICC(ratings, type = “agreement”)

The output will show the value of ICC.

Conclusion

Measuring agreement is essential in many research studies, and R provides useful tools to perform such statistical analysis. In this article, we have introduced popular functions in R used to measure agreement, including Cohen’s kappa, Kendall’s tau, and ICC. By using these functions, researchers can evaluate the level of agreement or concordance between multiple raters or observers and gain insights into their research data.