Author,Title,Edition,Publisher,Year,Series,Number,ISBN,ISSN,URL
"Arner, George B. L. and Truesdell, Leon E. and United States. Bureau of the Census","General report : unemployment by occupation, April, 1930, with returns from the special census of unemployment , January, 1931",,Ross Pub.,2003,Census of the United States,,0883545411,,https://cir.nii.ac.jp/crid/1130000796044804352