Seasonal adjustment usually attempts to correct for “expected” changes in employment level during the year. For example during the Christmas holiday season, lots of part-time workers are usually hired and then let go after New Year’s. To get a better sense of how the underlying economic trends go, BLS attempts to figure out how to strip out these sorts of yearly events and get to the “real” number of net jobs created or lost. The problem is that they have to use some cagey assumptions about how strong these yearly fluctuations are in a given year and can be slow to reflect changes in employment trends.
“Seasonal adjustment” means it is campaign season, with an election in 30 days. Economists were surprised because they expected the seasonal adjustment to result in a unemployment rate of 3.1%, but everyone who tried to apply the fudge factors either died laughing or collapsed in shock.
It explains how we can keep the same unemployment rate while losing lots of jobs.