Bell Curve Ð Which Test to Use?
nTest for ANY difference between means? - Two-tail
nTest < or > between means? - One-tail
n1. Rejection region - distribution above the critical value
n2. Errors
nType I -  rejecting true H0
nType II - accepting false H0
n3. Level of significance (α) - probability of making Type I
n4. Power of statistical test (1 - β) - probability of making  
n          the correct decision to reject false null