# Fleiss kappa in R giving strange results

I have an experiment where 4 raters gave their responses to 4 stimuli, and I need to calculate the Fleiss Kappa to check the agreements of the raters. However, I get strange results from the R function implementing the Fleiss analysis.

Participant1 <- c(16, 15, 16, 16)
Participant2 <- c(16, 16, 16, 16)
Participant3 <- c(16, 16, 16, 16)
Participant4 <- c(16, 16, 16, 15)
data <- data.frame(Participant1, Participant2, Participant3, Participant4)
data
library(irr)
kappam.fleiss(data)


The output is

> data
Participant1 Participant2 Participant3 Participant4
1           16           16           16           16
2           15           16           16           16
3           16           16           16           16
4           16           16           16           15

> kappam.fleiss(data)
Fleiss' Kappa for m Raters

Subjects = 4
Raters = 4
Kappa = -0.143

z = -0.7
p-value = 0.484


The value for kappa is negative and with a non-significant p-value, despite a clear agreement between raters. Why? Personally, I do not really get the answer to the similar question reported here: Strange values of Cohen's kappa

So, why is the Fleiss analysis useful? The results seem to me to not give an indication on how much raters agreed.

How can I simply calculate the agreement between the four raters?