A certain region would like to estimate the proportion of voters who intend to participate in upcoming elections. A pilot sample of 25 voters found that 21 of them intended to vote in the election. Determine the additional number of voters that need to be sampled to construct a 98?% interval with a margin of error equal to 0.04 to estimate the proportion.
Solution :
Given that,
n = 25
x = 21
= x / n = 21 / 25 = 0.84
1 - = 1 - 0.84 = 0.16
Margin of error = E = 0.04
At 98% confidence level the z is ,
= 1 - 98% = 1 -
0.98 = 0.02
/ 2 = 0.02 / 2 =
0.01
Z/2 =
Z0.01 = 2.326
Sample size = ( Z/2 /
E)2 *
* (1 -
)
= (2.326 / 0.04)2 * 0.5 * 0.5
= 454.46 = 455
The additional number of voters that need to be sampled is = 455
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