sentences:  He published his "magnum opus", "A Study of Saving in the United States", in 1955.This work, partly coauthored with Dorothy Brady and Horst Menderhausen, ran to three volumes totalling more than 2000 pages and included many hundreds of tables of time series data.These data were crucial for early empirical tests of the life cycle and the permanent income theories of consumption, as the official national income accounts for the USA begin only in 1929.