I am trying to do a chisq.test or a prop.test on data where some patients are surgical and other are non-surgical. I want to see if the proportions of the two sexes are equal in both groups. What is the most appropriate test in this instance where my surgical and non-surgical group sizes are not equivalent?
I am trying to use the following code, using data.table but I get the error also found below:
> chisq.test(lateral[Surgery == "No", "sex",with=F], lateral[Surgery == "Yes", "sex",with=F])
Error in chisq.test(lateral[Surgery == "No", "sex", with = F], lateral[Surgery == :
'x' and 'y' must have the same length
For prop.test():
Error in complete.cases(x, n) : not all arguments have the same length
Data
setDT(structure(list(sex = c(2L, 2L, 2L, 1L, 1L, 2L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 2L, 2L, 2L, 1L, 2L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 2L, 1L, 2L, 1L, 1L, 1L, 1L, 2L, 1L, 2L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 1L, 2L, 1L, 1L, 2L, 2L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 1L, 2L, 2L, 2L, 1L, 2L, 1L, 1L, 1L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 2L, 1L, 1L, 1L, 2L, 1L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 2L, 2L, 1L, 2L, 1L, 1L, 2L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 2L, 1L, 1L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 2L, 2L, 2L, 1L, 2L), Surgery = c("No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes" )), row.names = c(NA, -239L), class = c("data.table", "data.frame" )))
You can pass a table to the function chisq.test, making it more simple. For example
df <- structure(list(sex = c(2L, 2L, 2L, 1L, 1L, 2L, 1L, 1L, 1L, 2L,
1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 2L, 2L, 2L, 1L, 2L, 1L, 1L, 1L,
2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L,
1L, 1L, 2L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 2L, 1L, 2L, 1L, 1L, 1L,
1L, 2L, 1L, 2L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L,
2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L,
1L, 2L, 1L, 1L, 2L, 2L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 1L,
2L, 2L, 2L, 1L, 2L, 1L, 1L, 1L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 2L,
1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
2L, 1L, 2L, 1L, 1L, 1L, 2L, 1L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L,
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L,
2L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 2L, 2L, 1L, 2L, 1L, 1L, 2L, 1L,
1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 2L, 1L, 1L, 2L,
2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L,
2L, 2L, 2L, 1L, 2L), Surgery = c("No", "No", "No", "No", "No",
"No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No",
"No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No",
"No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No",
"No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No",
"No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No",
"No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No",
"No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No",
"No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No",
"No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No",
"No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No",
"No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No",
"No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No",
"No", "No", "No", "No", "No", "No", "No", "No", "No", "No", "No",
"No", "No", "No", "No", "No", "No", "Yes", "Yes", "Yes", "Yes",
"Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes",
"Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes",
"Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes",
"Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes",
"Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes",
"Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes",
"Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes",
"Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes",
"Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes"
)), row.names = c(NA, -239L), class = c("data.table", "data.frame"))
df$sex <- as.factor(df$sex)
df$Surgery <- as.factor(df$Surgery)
(prop_table <- table(df))
# Surgery
# sex No Yes
# 1 97 66
# 2 57 19
mod1 <- chisq.test(prop_table)
mod1
# Pearson's Chi-squared test with Yates' continuity correction
#
# data: prop_table
# X-squared = 4.7727, df = 1, p-value = 0.02892
str(mod1)
# List of 9
# $ statistic: Named num 4.77
# ..- attr(*, "names")= chr "X-squared"
# $ parameter: Named int 1
# ..- attr(*, "names")= chr "df"
# $ p.value : num 0.0289
# $ method : chr "Pearson's Chi-squared test with Yates' continuity correction"
# $ data.name: chr "prop_table"
# $ observed : 'table' int [1:2, 1:2] 97 57 66 19
# ..- attr(*, "dimnames")=List of 2
# .. ..$ sex : chr [1:2] "1" "2"
# .. ..$ Surgery: chr [1:2] "No" "Yes"
# $ expected : num [1:2, 1:2] 105 49 58 27
# ..- attr(*, "dimnames")=List of 2
# .. ..$ sex : chr [1:2] "1" "2"
# .. ..$ Surgery: chr [1:2] "No" "Yes"
# $ residuals: 'table' num [1:2, 1:2] -0.783 1.147 1.055 -1.544
# ..- attr(*, "dimnames")=List of 2
# .. ..$ sex : chr [1:2] "1" "2"
# .. ..$ Surgery: chr [1:2] "No" "Yes"
# $ stdres : 'table' num [1:2, 1:2] -2.33 2.33 2.33 -2.33
# ..- attr(*, "dimnames")=List of 2
# .. ..$ sex : chr [1:2] "1" "2"
# .. ..$ Surgery: chr [1:2] "No" "Yes"
# - attr(*, "class")= chr "htest"