Question

A random sample of 330 medical doctors showed that 164 had a solo practice.

(a) Let p represent the proportion of all medical doctors who have a solo practice. Find a point estimate for p. (Use 3 decimal places.)


(b) Find a 90% confidence interval for p. (Use 3 decimal places.)

lower limit
upper limit

Give a brief explanation of the meaning of the interval.

90% of the all confidence intervals would include the true proportion of physicians with solo practices.

10% of the confidence intervals created using this method would include the true proportion of physicians with solo practices.     

90% of the confidence intervals created using this method would include the true proportion of physicians with solo practices.

10% of the all confidence intervals would include the true proportion of physicians with solo practices.

(c) As a news writer, how would you report the survey results regarding the percentage of medical doctors in solo practice?

Report the confidence interval.

Report p̂.     

Report p̂ along with the margin of error.

Report the margin of error.

What is the margin of error based on a 90% confidence interval? (Use 3 decimal places.)

Answer 1

Solution :

Given that,

n = 330

x = 164

a) Point estimate = sample proportion = = x / n = 164 / 330 = 0.497

1 - = 1 - 0.497 = 0.503

b) At 90% confidence level

= 1 - 90%

=1 - 0.90 = 0.10

/2 = 0.05

Z/2 = Z0.05  = 1.645

Margin of error = E = Z / 2 * (( * (1 - )) / n)

= 1.645 (((0.497 * 0.503) / 330)

= 0.045

A 90% confidence interval for population proportion p is ,

± E

= 0.497 ± 0.045

= ( 0.452, 0.542 )

lower limit = 0.452

upper limit = 0.542

90% of the confidence intervals created using this method would include the true proportion of physicians with solo practices.

c) Report p̂ along with the margin of error

Margin of error = E = Z / 2 * (( * (1 - )) / n)

= 1.645 (((0.497 * 0.503) / 330)

= 0.045