DETERMINING THE NUMBER OF WORK SAMPLE OBSERVATIONS NEEDED. The manager of Michigan County’s welfare office, Dana Johnson, estimates that her employees are idle 25% of the time. She would like to take a work sample that is accurate within ±3% and wants to have 95.45% confidence in the results.
APPROACH \blacktriangleright Dana applies Equation (10-7) to determine how many observations should be taken.
n = \frac{z^2 p(1 - p)}{h^2} (10-7)