Employment data come from surveys!

Government statistics suffer from significant processing noise and shifting patterns of nonresponse biases (just like political polls)

People who don’t answer surveys cause biases in the things they measure. The methods researchers use to adjust for those biases can add further noise to those estimates.

These are two important facts of survey sampling that people too often forget. In politics, they mean pre-election polls can miss the mark because the people picking up the phone (or logging in to the computer) are systematically different than those who aren’t. Weighting by too many variables — like age, race, education, participation and the interactions between those — can also cause higher variance in a polls.

But nonresponse and statistical flukes also affect the surveys the government conducts to gauge things like hiring, the unemployment rate and labor-force participation. Sometimes, the biases from these factors can even be quite large.

Take December’s job report. Based on interviews conducted by the Bureau of Labor Statistics, the government estimated that about 200,000 jobs were added each in November and Decem…