A Gallup poll asked 1200 randomly chosen adults what they think the ideal number of children for a family is. Of this sample, 53% stated that they thought 2 children is the ideal number. Construct and interpret a 95% confidence interval for the proportion of all US adults that think 2 children is the ideal number.
Answer:
at 95% Confidence interval level: 0.501776 < p < 0.558224
Step-by-step explanation:
sample size n = 1200
population proportion [tex]\hat p[/tex]= 53% - 0.53
At 95% confidence interval level;
level of significance ∝ = 1 - 0.95
level of significance ∝ = 0.05
The critical value for [tex]z_{\alpha/2} = z _{0.05/2}[/tex]
the critical value [tex]z _{0.025}= 1.96[/tex] from the standard normal z tables
The standard error S.E for the population proportion can be computed as follows:
[tex]S,E = \sqrt{\dfrac{\hat p \times (1-\hat p)}{n}}[/tex]
[tex]S,E = \sqrt{\dfrac{0.53 \times (1-0.53)}{1200}}[/tex]
[tex]S,E = \sqrt{\dfrac{0.53 \times (0.47)}{1200}}[/tex]
[tex]S,E = \sqrt{\dfrac{0.2491}{1200}}[/tex]
[tex]S,E = 0.0144[/tex]
Margin of Error E= [tex]z_{\alpha/2} \times S.E[/tex]
Margin of Error E= 1.96 × 0.0144
Margin of Error E= 0.028224
Given that the confidence interval for the proportion is 95%
The lower and the upper limit for this study is as follows:
Lower limit: [tex]\hat p - E[/tex]
Lower limit: 0.53 - 0.028224
Lower limit: 0.501776
Upper limit: [tex]\hat p + E[/tex]
Upper limit: 0.53 + 0.028224
Upper limit: 0.558224
Therefore at 95% Confidence interval level: 0.501776 < p < 0.558224
