OE
The chart shows defective parts per 1,000 as a function of machine operator experience. The dots indicate individual machine operators, and there is quite a bit of variance by individual. The line labeled “Average” shows the average performance of the group as a whole. A trend emerges: inexperienced machine operators and very experienced machine operators make Fewer mistakes than those with medium level of experience. Also, certain individual machine operators produce defective parts at a lower rate than others with similar levels of experience.
Because the question specifies “on average,” refer to the curve marked “Average” rather than the individual data points. At the lowest point on this average curve, operators with 16,000 hours of experience produce slightly fewer than 25 defective parts per 1,000. Another low point is for operators with minimal experience, but even they produce between 25 and 30 defective parts per 1,000. In contrast, the defective part rate is maximized at the top of the curve: operators with 8,000 hours of experience produce about 40 defective parts per 1,000.