Question

2. A group of 35 subjects took an IQ test during part of a study. The subjects had a standard deviation IQ score of 14.2.(12 points)a) Find the critical values and corresponding to a 99% level of confidence.b) Construct a 99% confidence interval estimate of σ, the standard deviation of the population.

Answer 1

We use chi -dist to find the confidence interval for the population SD. But we start by find the interval for the variance. Then taking the square root to get the SD.

(1 - )% confidence interval for population variance

Where = 1- 0.99 = 0.01

The df = n-1

= 34 .................n =35

Sx^2 = sample variance

= 14.2 * 14.2

=201.64

Two critical values are calculated using chi-square tables

Lower L. =

= 58.9639

Upper L. =

= 16.5013

Substituing the values we have

(116.2704,415.4686) for the variance

For SD

This means we 99% confidence that the true population SD lies within this calculated interval.

answered by: anonymous