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Research designs

Research designs. by Willem E.SARIS. literature. Saris W.E. Kollege dictaat Saris W.E. and H. Stronkhorst Introduction to causal modelling Extra reading on causality Winship C. and S.L.Morgan The estimation of causal effects from observational data. Annual Review of Sociology 1999.

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Research designs

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  1. Research designs by Willem E.SARIS

  2. literature • Saris W.E. Kollege dictaat • Saris W.E. and H. Stronkhorst Introduction to causal modelling • Extra reading on causality • Winship C. and S.L.Morgan The estimation of causal effects from observational data. Annual Review of Sociology 1999 college titel en nummer

  3. Different classifications of designs An Overview

  4. EXPERIMENTS IN PHYSICS • 1. physical manipulation : change of pressure, change of temperature etc • 2. physical control of other variables: isolation, insulation, sterilization, sound proofing, etc. college titel en nummer

  5. Research design • o(1) x o(2) • Difference of observation 0(2) and 0(1) indicates a possible effect of the manipulation (x). • PHYSICAL CONTROL excludes other explanations for differences in observations before and after manipulation. college titel en nummer

  6. EXPERIMENTS IN AGRICULTURE • In order to test the quality of a fertiliser a test is done in a field. • The field is divided in two parts: One is treated with the old and the other with the new fertiliser college titel en nummer

  7. ALTERNATIVES FOR CONTROL • Physical control is often not possible. • As a substitute is used : • RANDOM ASSIGNMENT college titel en nummer

  8. Why Random assignment • By such a random procedure the average value for each condition is expected to be the same at the start. • RANDOM ASSIGNMENT prevents all alternative explanations like differences in soil, temperature, water etc. college titel en nummer

  9. THE FERTILISER EXAMPLE • The field is divided in many small parts. • Each part is randomly assigned to treatment with the old or the new fertiliser. college titel en nummer

  10. The Argument • If the fertilizers were equally good, the average crop per unit would be the same in the experimental and the control group. • x(1) o(1) • x(2) o(2) • Difference in crop [o(2) - o(1)] can only be due to differences between the fertilizers • Except for …. ? college titel en nummer

  11. Experiments in Psychology • In psychological laboratory experiments test persons are randomly assigned to the experimental group or the control group • Then the situation is manipulated by providing the two groups with different treatments • The means (proportions) of the opinions or behavior are compared college titel en nummer

  12. EXPERIMENTS IN SOCIAL SCIENCES • Physical control is hardly used. • Manipulation is more often possible • Random assignment is seldom possible college titel en nummer

  13. Problems • If random assignment is not used then the groups are NON-EQUIVALENT. • This means that they differ not only in the treatment but also in other characteristics • So the effect can also be explained by other factors. college titel en nummer

  14. CLASSIFICATION OF DESIGNS • Use of manipulation not • randomization 1 - • not 2 3 college titel en nummer

  15. Design 1 • experimental designs • - with manipulation and • - randomization • Mainly used in psychology, communication research but recently also in political sciences and economy college titel en nummer

  16. Design 2 • quasi experimental designs: • - with manipulation • - no randomization • Mostly used in educational research college titel en nummer

  17. Design 3 • Observational studies: • - no manipulation • - no randomization • Used in all social sciences college titel en nummer

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