% within x SDs of mean question

DavidC · #1 08-04-2005, 04:16 AM

I'm curious... how much % of the curve on a standard distro is within 1 SD of the mean?

2 SD?

3 SD?

(My guess: 67/90/95, or 67/99/99.5)

emp1346 · #2 08-04-2005, 04:25 AM

in a standard normal distribution with a mean of zero,

1 SD: .3413 or +/- 1 SD: .6426
2 SD: .4772 or +/- 2 SD: .9544
3 SD: .4987 or +/- 3 SD: .9974

As an additional note, that's why Six Sigma is so common in business applications, because it represents 99.74% of the distribution...