In: Statistics and Probability
In 625 at bats a baseball player got a hit 28% of the time. Find a 95% confidence interval for the true percentage of time he gets a hit.
Solution :
Given that,
n = 625
Point estimate = sample proportion = = 0.28
1 - = 1-0.28=0.72
At 95% confidence level
= 1 - 95%
= 1 - 0.95 =0.05
/2
= 0.025
Z/2
= Z0.025 = 1.96 ( Using z table )
Margin of error = E = Z / 2 * (( * (1 - )) / n)
= 1.96 (((0.28*0.72) / 625)
E = 0.0352
A 95% confidence interval for population proportion p is ,
- E < p < + E
0.28-0.0352 < p < 0.28+0.0352
0.2448< p < 0.3152
The 95% confidence interval for the population proportion p is : 0.2448, 0.3152