Question

Out of 400 people sampled, 248 had kids. Based on this, construct a 95% confidence interval for the true population proportion of people with kids.

Give your answers as decimals, to three places

< p <

Answer 1

Solution :

Given that,

n = 400

x = 248

Point estimate = sample proportion = = x / n = 248/400=0.62

1 -   = 0.38

At 95% confidence level the z is ,

= 1 - 95% = 1 - 0.95 = 0.05

/ 2 = 0.05 / 2 = 0.025

Z/2 = Z0.025 = 1.96   ( Using z table )

Margin of error = E = Z/2   * ((( * (1 - )) / n)

= 1.96 (((0.62*0.38) / 400)

E = 0.048

A 95% confidence interval for population proportion p is ,

- E < p < + E

0.62-0.048 < p < 0.62+0.048

0.572<p<0.668