Normal Distribution

α = tail area	central area = 1 – 2α	zα
0.10	0.80	z.10 = 1.28
0.05	0.90	z.05 = 1.645
0.025	0.95	z.025 = 1.96
0.01	0.98	z.01 = 2.33
0.005	0.99	z.005 = 2.58