Barry Eichengreen’s and Tim Hatton’s January 1988 paper entitled “Interwar Unemployment in International Perspective” is a useful starting point for any effort to compare unemployment during the Great Depression and the Great Recession.
It is useful to begin by recognizing three related cautions that the authors make in that paper. First, the modern sense of the term “unemployment” (willing and able to work, but unable to find a job commensurate with the worker’s skills) was not common until the decades before the Great Depression. The prior assumption was that people were unemployed because they were lazy. There was little understanding of business cycles or inadequate demand, little sympathy for the unemployed, and no sense that business or government were primarily responsible for the the level of unemployment. This meant that keeping data on unemployment was rarely a concern of government. Data on unemployment in Europe was largely collected through industrial trade unions.