For one thing BLS has the notion of "discouraged workers".
These are folks that have given up and aren't even looking for a job. They are not counted as unemployed! That's why even when new jobs shoot up the unemployment numbers as a percentage often don't change. The discouraged workers start looking again and then are suddenly counted as unemployed.
Alex
"There is a cult of ignorance in the United States, and there has always been. The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that "my ignorance is just as good as your knowledge."
-- Isaac Asimov