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EXPERIMENTAL DESIGN

EXPERIMENTAL DESIGN

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EXPERIMENTAL DESIGN

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  1. EXPERIMENTAL DESIGN Experimental and Pre (Quasi) Experimental Designs

  2. Basic Issues in Experimental Design • Manipulation of the Independent Variable • Selection of the Dependent Variable • Assignment of subjects (or other test units) • Control over extraneous variables

  3. Manipulation of the Independent Variable • In a classical experiment, the researcher measures the condition of the subjects – both treatment and control groups - on the dependent variable and then “manipulates” the independent variable for the “treatment group” while not “manipulating” that variable for the “control” group, and then “re-measures the dependent variable for both groups while controlling “all other variables”.

  4. Artificial – Low Realism Few Extraneous Variables High Control Low Cost Short Duration Subjects Aware of Participation Natural – High Realism Many Extraneous Variables Low Control High Cost Long Duration Subjects Aware of Participation Laboratory vs Field Experiments

  5. “ONE-SHOT” CASE STUDY T1 T2 T3 X O Where: X = Treatment O = Observation

  6. How good is this research design? • Scientifically it is not good at all • However, that the classical case studies in all of the social sciences have contributed more to those discipline’s knowledge than any other design • First – much of the pioneer work that shaped the social sciences was accomplished before the advent of sophisticated research designs • Second –research is always the enterprise of individuals and individual skill can “substitute” for sophisticated design controls • Third – research designs which require sophisticated controls are limited to different kinds of inquires

  7. “ONE-GROUP” PRETEST - POSTTEST T1 T2 T3 O X O

  8. “STATIC GROUP” COMPARISON T1 T2 T3 X O O

  9. “PRETEST - POSTTEST”CONTROL GROUP DESIGN T1 T2 T3 Trt O X O Ctrl O O

  10. Posttest-Only Control Group T1 T2 T3 O X O O

  11. “SOLOMON” FOUR - GROUP DESIGN T1 T2 T3 O X O O O X O O

  12. More Complex Experimental Designs • Completely randomized designs • Randomized block design • Factorial design • Latin square design

  13. Experimental Conditions • Double Blind experiment – neither “observer” nor the “subjects” know whether the subject are in the treatment or control groups or receiving a placebo. • Placebo effect – One experimental group is given the “treatment” that is being tested while another “treatment” group receives a “treatment” but one that is, by design, “benign” in its effect.

  14. Extraneous Variables • History • Maturation • Testing • Instrumentation • Selection • Mortality

  15. Extraneous Variables • History – specific events in the environment between the before and after measurement that are beyond the experimenter’s control e.g. a major employer closes its plant in a test market area • Maturation – subjects change during the course of the experiment e.g. subjects become tired

  16. Extraneous variables(cont -2) • Testing – the before measurement alerts subject to the nature of the experiment • e.g. questionnaire about traditional role of women triggers enhanced awareness of women in the experiment • Instrumentation – changes in measuring instrument result in response bias • e.g. new questions about women are interpreted differently than earlier questions

  17. Extraneous variables(cont -3) • Selection – sample selection error occurs because of differential selection of comparison groups • e.g. control and experimental groups are assigned self-selecting groups based on preference for soft drinks • Mortality – sample attrition, some subjects withdraw from experiment • e.g. subjects in one group of students withdraw from school

  18. Control for Extraneous Variation • Eliminate Extraneous Variables • Hold Conditions Constant • Randomization • Matching Subjects

  19. Demand Characteristics • Design procedures that “hint” to subjects about the experimenter’s hypothesis • Guinea Pig effect – when subjects exhibit behavior that they feel is expected of them • Hawthorne effect – causes people to perform differently just because they know they are experimental subjects

  20. Problems of Internal Validity

  21. Ethical Issues • Harm • “Unfair benefit” • Privacy • Confidentiality • Deception • Not using debriefing