Error message when using "car" package

[Novlette]

I keep getting error messages whenever I download "car" package to perform a levene test
#Open data file

data(mtcars)
#Check for equal variances
library(car)
leveneTest(mtcars$qsec_before~as.factor(mtcars$am))
Error in model.frame.default(form) :
invalid type (NULL) for variable 'mtcars$qsec_before'

[andresrcs]

@Novlette

mtcars$qsec_before

The mtcars data set doesn't contain a variable called qsec_before and you are not defining it anywhere in your code, that is why you get the NULL error, you should check on that.

names(mtcars)
 [1] "mpg"  "cyl"  "disp" "hp"   "drat" "wt"   "qsec" "vs"   "am"   "gear" "carb"

[Novlette]

Thanks for your quick reply. I am a newbie at this, I am trying to test the distribution of automatic and manual transmission. qsec represents the quater mile time of various cars