He ended up at the Census Bureau and took classes at the Graduate School of the U.S. Department of Agriculture and at American University where he took courses from W. Edwards Deming and Meyer Abraham Girshick.

“Before that the Census Bureau had the idea that they couldn’t do sampling because that would discredit the results; they had to have complete coverage.”[1] This experience encouraged the Works Progress Administration beginning in 1940 to sponsor the development of a monthly sample survey of households to provide estimates of employment and unemployment, later known as the Current Population Survey.

His papers with William N. Hurwitz[2][3][4] are viewed as foundational building blocks for later developments in design-based sampling theory.

After retiring from the Census Bureau, Hansen joined Westat, a private research firm in Rockville MD USA, as a vice president in 1968.

In 1983, while at Westat, he, Tepping, and Madow published an important contribution to an ongoing controversy among researchers in sampling theory and estimation on the role of models in making inferences from survey data.