Propoion of area from middle of curve to +1 standard detion-
Ref:Parks 23rd edition pg 849. 1SD : confidence limit = 68% 2SD : confidence limit = 95% 3SD : confidence limit = 99.7% +/- 1SD: includes 68% of values, so +1SD will include half of it = 34%
0.68
0.17
0.12
0.34
Biostatistics