I'm just new in the field of t.tests so I thought I will make some excersises, but the point I can't get clear is when to use a lower or upper tail t.test. For example the following example:
3 people which have high blood pressure get a medicine for a period of 4 weeks to lower the blood pressure.
What I think when I read this is:
- $H_0$: blood pressure keeps the same
- $H_A$: blood pressure gets LOWER
So I would think I have t use a t.test whith lower tail(I think it's called this way), I work in R the most of the time so I would use
alt = "less". But according to my teacher it sould be
alt="greater", but why?