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
At 95% confidence level the z is ,
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 ,
0.601-0.029 < p < 0.601+0.029
(0.572, 0.63)