what is probability?
measure of how likely it is that some event will occur
what is a type 1 error
reject null when we should not
what is a type 2 error?
fail to reject the null when we should
why is the alpha level 0.05?
our inference is wrong 5% time
find significance wrongly 5 times / 100
why can’t reduce the alpha level?
decreasing likelihood of type 1 error increase likelihood of type 2 error
what is directional hypothesis
one tailed
usually based on previous research
what is a non directional hypothesis?
two tailed
no predicition on results