Day, R. A., & Underwood, A. L. 1. (1991). Quantitative analysis (6th ed.). Prentice Hall Intenational.
Lua i Stíl Chicago (17ú heag.)Day, Reuben Alexander, agus Arthur Louis 1924 Underwood. Quantitative Analysis. 6th ed. Englewooe Cliffs, NJ: Prentice Hall Intenational, 1991.
Lua MLA (9ú heag.)Day, Reuben Alexander, agus Arthur Louis 1924 Underwood. Quantitative Analysis. 6th ed. Prentice Hall Intenational, 1991.
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