Question

A local school board member randomly sampled private and public high school teachers in his district to compare the proportions of National Board Certified (NBC) teachers in the faculty. The results were:

Answer 1

0.025 ;

(-0.7198 ; 0.7698)

Explanation:

From the table :

_____________ private schls ___ public schls

Sample size, n _____ 80 __________ 520

P, NBC teachers ___ 0.175 ________ 0.150

P1 = P of private school teachers

P2 = P of public school teachers

Difference in proportion :

P1 - P12 = 0.175 - 0.150.= 0.025

The 90% confidence interval for 2 - sample proportion :

C.I = (p1-p2) ± [Zcritical * √(p1(1-p1)/n1 + (p2(1-p2)/n2)]

Zcritical at 90% = 1.645

C.I = 0.025 ± [1.645 * √((0.175*0.825)/80 + (0.150*0.850)/520)]

C.I = 0.025 ± [1.645 * √(0.0018046875 + 0.0002451)]

C.I = 0.025 ± 1.645 * 0.0452755

C.I = 0.025 ± 0.07448

C.I = (-0.7198 ; 0.7698)