CohenJ.Statistical Power Analysis for the Behavioral Science.Hillsdale: NJ Lawrence Erlbaum Associates, 1988.
2.
HeberleinT.A., BaumgartnerR.Factors affecting response rates to mailed questionnaires: A quantitative analysis of the published literature. Amer Soc Rev1978; 43: 447–62.
3.
CohenJ., CohenP.Applied Multiple Regression/Correlation Analysis for the Behavioral Sciences.Hillsdale: NJ Lawrence Erlbaum Associates, 1983.
4.
PolitD.G., HunglerB.P.Nursing Research: Principles and Methods, 5th edition. Philadelphia PA: JB Lippincott Company, 1995.
5.
PolitD.F., HunglerB.P.Nursing research: Principles and methods, 5th edition. Philadelphia PA: JB Lippincott Company, 1995.
6.
BaileyD.M.Research for the Health Professional: A Practical guide.1991. F.A. Davis, Co., Philadelphia.
7.
HulleyS.B., DummingsS.R.Designing Clinical Research.Williams and Wilkins.Baltimore, MD.1988
8.
OkoloEnHealth Research Design and Methodology.1990. CRC Press, Inc., Boca Raton, FL.