calculate the variance of the given vector
not sure how to get the unit tests working. or make it less obvious to the user
c(52,73,55,26,72,45,80,62,NA,7,NA,87,54,46,85,37,94)
test_that("Variance", {
expect_equal(round(var(c(52,73,55,26,72,45,80,62,NA,7,NA,87,54,46,85,37,94),na.rm=T),4),round(587.5238,4))
})