Question

A shipment of 375 new blood pressure monitors have arrived. Tests are done on 65 of the new monitors and it is found that 12 of the 65 give incorrect blood pressure readings. Find the 95% confidence interval for the proportion of all the monitors that give incorrect readings.

Answer 1

Sample proportion of monitors that give incorrect readings, p = 12 / 65 = 0.1846

For a finite population size of N = 375, Standard error of proportion is,

= 0.0438

Z value for 95% confidence interval is 1.96

Margin of error = z * SE = 1.96 * 0.0438 = 0.0858

95% confidence interval for the proportion of all the monitors that give incorrect readings is,

(0.1846 - 0.0858,  0.1846 + 0.0858)

(0.0988 ,  0.2704)