Use the zscore to solve this problem and to judge whether an

Use the z-score to solve this problem and to judge whether an event is usual or not usual.

Among workers subjected to injurious fibers called asbestos in a shipyard in 1980, 33 people passed away over a period of 10 years from lung disease, whereas only 24 such deaths would be expected based on statewide mortality rates.

Is the number of deaths from COPD in this group excessive?

Show your work clearly and thoroughly as if you are explaining it to a person who is a dummy.

Solution

Using z score method, Xi=33 Xbar=24 and s=10.

z=(Xi-Xbar)/s

z=(33-24)/10

z=0.9

Find the area corresponding to the z score. The value is 0.8159. This is the required proportion. The proportionis quite high and this shows that the death is excessive.