Binary t-Test Order

Question

I'm performing a t-test for some simple data. The data I imported (plant.growth) had column one (pesticide) has whether the plant received pesticide A or B and column two had the amount grown in inches (height).

When I run the t test, t.test(height~treatment), my t-value and my confidence intervals are negative. I would prefer them to be positive but I don't know how to get the binary data to flip (ie have the sample mean of A be subtracted from the sample mean of B. I'm still really new to R, and I can't seem to find a simple way to do this.

Thank you for your help!

Answer 1

treatment <- relevel(treatment, ref = "B")
t.test(height ~ treatment)

Or alternatively

treatment <- factor(treatment, levels=c("B","A"))

would also have worked.