We have a sophisticated printing business with machines that do many different printing, folding, cutting and other operations, making packaging materials for comsumer products. We have 30 percent turnover among machine operators and hope to reduce that by hiring higher quality personnel. Much of the turnover occurs because several other persons we've been hiring have made mistakes in trying to run the machines, in spite of training, and were terminated. We could use interviews, asking questions we think will reveal spatial aptitude, such as whether the applicant learned to ride a bike before age 6, or can ice skate, or liked art classes in school. Or we can use a test, say, one consisting of 30 problems, such as drawings of machinery or two dimensional objects with related questions.
Research shows that good tests are more reliable than interviews for making measurements.
What this means is that the test will give us just one number, say an 8, and that if we tested the person again on this or a similar good test we'd get another 8 or a 7 or 9. In contrast, if we asked 6 different interviewers to listen to the applicant's responses to the same set of questions, such about interest in art classes, we would almost certainly get scores ranging much wider than from 7 to 9. You'll almost certainly get a rather wide range of responses, just as I did when I asked my business friends to rate me on verbal aptitude. Now, return in your mind to our initial chart. We know that a 10 on spatial aptitude will likely correspond to work performance between 8 and 10.