The approximate 95 % confidence interval for p is found by the formula
p^ ± Z∝/2 √p^q^/n
The sample size n can be found by the
The formula
n= (Z∝/2)² p^q^/e²
The approximate 95 % confidence interval for p is 0.165; 0.243
This indicates 95 % confidence interval level.
A sample of 6239 nonprofits should be surveyed
Solution
Part a:
Sample Proportion p^= 84/412= 0.2038 ≅ 0.204
q^ = 1-p^= 1.0 -0.204= 0.796
The degree of confidence is 95% so z∝/2= 1.96
Putting the values
p^ ± Z∝/2 √p^q^/n
0.204 ± 1.96 √0.204(0.796)/ 412
0.204 ± 0.0389
0.1650 ; 0.2429
0.165; 0.243
The approximate 95 % confidence interval for p is 0.165; 0.243
Part B
This indicates 95 % confidence interval level.
Part C
With ± 0.01 of 0.95 Confidence interval gives range 0.94 to 0.96
For 0.96 interval Z∝/2 = 2.054
For 0.94 interval Z∝/2 = 1.8808
and error e= 0.01
For solving n the formula is
n= (Z∝/2)² p^q^/e²
and e= 0.01
Putting the values
n= 1.96²(0.204)(0.796)/ 0.01²
n= 6238.1437≅ 6238.14
A sample of 6239 nonprofits should be surveyed.
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