Caution should be used in accepting conclusions from a research study with problems of selection and an ex post facto design (Smith, 1968).
References
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CampbellD. T.StanleyJ. C.Experimental and quasi-experimental designs for research on teaching. In GageN. L. (Ed.), Handbook of research on teaching. Chicago: Rand McNally, 1963. Pp%. 240–241.
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KerlingerF. N.Foundations of behavioral research. New York: Holt, Rinehart, & Winston, 1964.
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SmithM. P.Intellectual differences in five-year-old underprivileged girls and boys with and without pre-kindergarten school experience. Journal of Educational Research, 1968, 61, 348–350.
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WinerB. J.Statistical principles in experimental design. New York: McGraw-Hill, 1962.
