14 out of 20 covid samples came back positive. find a 90% confidence interval for the proportion who are negative.
solution
Point estimate = sample proportion = = x / n = 14/20=0.7
1 - = 0.3
At 90% confidence level the z is
= 1 - 90% = 1 - 0.90 = 0.1
/ 2 = 0.1 / 2 = 0.05
Z/2 = Z0.05 = 1.645 ( Using z table )
Margin of error = E Z/2 * (( * (1 - )) / n)
= 1.645 *((0.7*0.73) /20 )
= 0.169
A 90% confidence interval is ,
- E < p < + E
0.7-0.169 < p < 0.7+0.169
0.531< p < 0.869
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