=+9.71 When n is large, the statistic s is approximately unbiased for estimating s and has approximately a normal distribution. The standard deviation of this statistic when the population distribution is normal is which can be estimated by . A large-sample confidence interval for the population standard deviation s is then s 6 1z critical value2 s

12n s

12n ss <

s 12n x 1 2.33 s

1n m , x 1 2.33 s

1n