Observation

Agnew, Neil McK. and Sandra W. Pyke
[1969] The Science Game, An Introduction to Research in the Behavioral Science, Prentice-Hall, Englewood Cliffs, New Jersey

Bernard, Claude
[1865]  Introduction à l'étude de la médecine expérimentale, Garnier-Flammarion, Paris, 1966

Beveridge, W. I. B.
[1950]  The Art of Scientific Investigation, Random House Vintage Books, New York, 1957

Caws, Peter
[1965]  The Philosophy of Science, D. Van Nostrand, Princeton, New Jersey

Kaplan, Abraham
[1964]  The Conduct of Inquiry. Methodology for Behavioral Science, Chandler Publishing Company, Scranton, Pennsylvania

Madge, John
[1953]  The Tools of Social Science, Longmans, London, 1965

Van Dalen, Deobold B.
[1962]  Understanding Educational Research. An Introduction, Mc-Graw-Hill Book Co., New York, 1979