I am having the following data (as an example). I am interested in measuring the difference in sentences between several texts in English and in Spanish. I can do that either with Mann-Whitney U and then calculate the R (effect size) or use biserial correlation. The differences between the text however are probably affected by two other variables related to the language. Can I implement these variables in a partial correlation test? Is it even acceptable that the controls are dichotomous in the form that they are in my example?
I managed to use a pcor script with a slight modification (instead of using scale I use pseudoinverse). I do receive a result but I wonder, if there is another method that can give me an effect size while controlling for these variables?
df = data.frame(case = c(1,1,2,2,3,3), language = c("en","es","en","es","en","es"),sents = c(100,200,250,300,350,340),
control_sents = c(10,12,10,12,10,12), control_userpower = c(5,10,5,10,5,10))
source("pcor.R")
pcor.test(df$language,df$sents,df[,c("control_userpower","control_sents")],use="mat")