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EXPERIMENTAL DESIGN

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

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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

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