In: Statistics and Probability
In a survey, 668 out of 1112 people said they support Medicare for all. Find the rule of thumb 95% confidence interval estimate of the true proportion of supporters.
Solution :
Given that,
n = 1112
x = 668
Point estimate = sample proportion = = x / n = 668/1112=0.601
1 - = 1- 0.601 =0.399
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 (((0.601*0.399) /1112 )
E = 0.029
A 95% confidence interval for population proportion p is ,
- E < p < + E
0.601-0.029 < p < 0.601+0.029
(0.572, 0.63)