Question

What's the difference between a one-sided and two-sided test?

Answer 1

We're learning about p-values and confidence intervals. My lecture notes all of sudden started talking about one-sided and two-sided tests. Can someone please explain what these are? Thanks.

Answer 2

I'll just give like a rough vague explanation, let me know if it helps at all of if you want me to be more thorough.

one sided or 2 sided depends on on what region you are considering, for example lets say t was the variable in question

something like t>x is one sided, because you are only concerned with whether it is greater than some value x, ie to the right of that value

but sometimes you get things like |t| > x
but |t|> x implies that t>x or -t<-x

which is 2 sided since the values we want may be on the left or right side.