Measurement is the process of turning concepts like length or employment status into precisely defined variables. Using a tape measure to turn the idea of “length” into a number is straightforward because we know exactly what we mean by length. Measuring college readiness is controversial because it isn’t clear exactly what makes a student ready for college work. Using SAT scores at least says exactly how we will get numbers. Measuring leisure time requires that we first say what time counts as leisure. Even counting highway deaths requires us to say exactly what counts as a highway death: Pedestrians hit by cars? People in cars hit by a train at a crossing? People who die from injuries six months after an accident? We can simply accept the government’s counts, but someone had to answer those and other questions in order to know what to count. For example, to be included the Fatality Analysis Reporting System, “a crash must involve a motor vehicle traveling on a trafficway customarily open to the public and must result in the death of at least one person (occupant of a vehicle or a non-motorist) within 30 days of the crash.” The details of when a death is counted as a highway death are necessary because they can make a difference in the data.
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EXAMPLE 3 Measuring unemployment
Each month the Bureau of Labor Statistics (BLS) announces the unemployment rate for the previous month. People who are not available for work (retired people, for example, or students who do not want to work while in school) should not be counted as unemployed just because they don’t have a job. To be unemployed, a person must first be in the labor force. That is, the person must be available for work and looking for work. The unemployment rate is
To complete the exact definition of the unemployment rate, the BLS has very detailed descriptions of what it means to be “in the labor force” and what it means to be “employed.” For example, if you are on strike but expect to return to the same job, you count as employed. If you are not working and did not look for work in the last two weeks, you are not in the labor force. So, people who say they want to work but are too discouraged to keep looking for a job don’t count as unemployed. The details matter. The official unemployment rate would be different if the government were to use a different definition of unemployment.
The BLS estimates the unemployment rate based on interviews with the sample in the monthly Current Population Survey. The interviewer can’t simply ask, “Are you in the labor force?” and “Are you employed?” Many questions are needed to classify a person as employed, unemployed, or not in the labor force. Changing the questions can change the unemployment rate. At the beginning of 1994, after several years of planning, the BLS introduced computer-assisted interviewing and improved its questions. Figure 8.1 is a graph of the unemployment rate that appeared on the front page of the BLS monthly news release on the employment situation. There is a gap in the graph before January 1994 because of the change in the interviewing process. The unemployment rate would have been 6.3% under the old system. It was 6.7% under the new system. That’s a big enough difference to make politicians unhappy.