CODEWITHSUNDEEP
rstatistical-test
Alex
Alex

Reputation: 33

R - how to get data into block form for friedman test?

enter image description hereI have some data relating to levels of a chemical in the blood before and after treatment and there are 4 treatment groups - ABCD. I have been told I can run a Friedman test to compare all of these variables at once. The code I've tried is:

attach(LiverData.Wide)
friedman.test(ALPB ~ ALPM | Group)

I get this error:

Error in friedman.test.default(c(80L, 37L, 52L, 36L, 39L, 48L, 71L, 81L,  : 
not an unreplicated complete block design

so I need to work out how to get the data into block form so that I can run the test - any ideas how?

NB: I am a novice at R so sorry for a very basic question!

Also, I am only focusing on ALPB and ALPM - I am not interested in the other columns

Upvotes: 3

Views: 3053

Answers (1)

StupidWolf
StupidWolf

Reputation: 46908

It requires an unreplicated data, meaning if you have replicates, you either summarize them or consider the observation as a block

For example:

LiverData.Wide = data.frame(
obs=rep(1:10,4),
APLB = rnorm(40,rep(1:4,each=10),1),
APLM = rnorm(40,rep(2*(1:4),each=10),1),
Group = rep(c("A","B","C","D"),each=10)
)

Then you average the measurement per group and test the difference between APLB and APLM using a matrix:

sumData = aggregate(APLB ~ APLM_grp + Group,data=LiverData.Wide,mean)
friedman.test(as.matrix(sumData[,2:3]))

Or if you consider observation as a block:

friedman.test(as.matrix(LiverData.Wide[,2:3]))

Upvotes: 3

Related Questions