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Experimental Research ( 實驗法 )

Experimental Research ( 實驗法 ). Social Research Methods 2117 & 6501 Fall, 2006 December 18-21, 2006. Experiments. Its greatest strength: enabling researchers to testing causal relationships ( 優點 : 可以探究因果關係 ) conform more to a positivist approach.

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Experimental Research ( 實驗法 )

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  1. Experimental Research (實驗法) Social Research Methods 2117 & 6501 Fall, 2006 December 18-21, 2006

  2. Experiments Its greatest strength: enabling researchers to testing causal relationships (優點: 可以探究因果關係) conform more to a positivist approach

  3. Research Questions Appropriate for Experiments • Well suited for relatively limited and well-defined concepts and propositions (適合範圍有限，定義清楚的概念和命題) • Appropriate for hypothesis testing, but only for one or a few causal variables • Micro-level questions: individual or small group phenomena

  4. Experimental Design Logic • Learn the language of experiments first: • Subjects (受試者) • Treatment (independent variable) and dependent variables • Pretest and posttest (前測與後測) • Experimental and control group • Random assignment (隨機分配)

  5. Selecting Subjects for Experiments: Random Assignment • Random assignment: random in a statistical sense (equal chance of being selected) • Why random assignment? • To make comparisons • Generalizability (概推性) • Unbiased • Make experimental and control groups comparable

  6. random assignment and random sampling

  7. How to randomly assign?

  8. Matching (配對) • Similar to quota sampling • Note: the overall average description of the experimental group should be the same as that of the control group • Comparable on what variables? Usually those related to the dependent variable under study

  9. Matching

  10. Matching or Randomization (隨機化)? • The case for randomization: • Don’t know which variables for the matching. • Statistics used for analyzing experiment results assume randomization • But with only a few subjects, matching would be better. • Can combine matching and randomization • Ex: create strata

  11. Types of Experimental Design • Again, components of classical experimental design (古典實驗法的三個要素) :

  12. Preexperimental Designs • One-shot case study (單組個案研究) • A single group of subjects, experimental stimulus • One-group pretest-posttest design (單組前後測設計) • Other factors may cause changes between pretest and posttest • Static-group comparison (靜態組間比較) • Experimental and control groups, but no pretest

  13. Preexperimental Research Designs

  14. Quasi-Experimental Designs: Solomon four-group design (所羅門四組設計)

  15. Quasi-Experimental Designs Posttest-only group design (後測控制組設計) • Contains only group 3 and 4 in the Solomon design • Randomly assigning subjects to experimental and control groups • Randomization: make subjects comparable on the dependent variable

  16. Design Notation • O = observation of dependent variable • X = treatment (independent variable) • R = random assignment • Symbols in time order: from left to right • O1 = pretest, O2 = posttest • See Table 9.2 (p. 261)

  17. A Comparison of Various Experimental Design

  18. Validity Issues in Experimental Research • internal validity (內在效度): the hypothesized independent variable alone affects the dependent variable. (以實驗設計排除自變數已外的變項， 只有自變數影響了依變數。)

  19. Threats to internal validity • Selection bias (選擇偏差) • History • Maturation • Testing • Instrumentation (測量工具)(related to measurement) • Experimental mortality (實驗流失)(subjects drop out) • Statistical regression (involving extreme cases) • Diffusion of treatment or contamination • Compensatory behavior (補償行為) • Experimenter expectancy (實驗者期望)

  20. The double-blind experiment (雙盲實驗) Neither the subjects nor the experimenters know which is the experimental group and which is control. (受試者與實驗者都不知誰是對照組或控制組)

  21. The double-blind experiment

  22. External validity (外在效度) • External validity: the ability to generalize experimental findings to events and settings outside the experiment itself (實驗發現可以概推到現實世界) • Campbell and Stanley: the interaction between the testing situation and the experimental stimulus (測驗情境與實驗刺激產生交互作用) • Can use Solomon four-group design to address this interaction problem

  23. External validity: reactivity (實驗反應) • Reactivity: subjects are aware of that they are in an experiment and being studied • Hawthorne effect (霍桑效應: 受試者的反應其實是針對研究者對他們的關注) • Demand characteristics • Placebo effect

  24. Ethical Concerns in Experimental Research • Experiments are intrusive (實驗介入性高，影響到受試者) • Deception (欺騙): dishonesty is acceptable only as the means to achieve a goal that cannot be achieved otherwise • Debriefing needed

  25. Strengths and Weaknesses of Experiments • Strengths • The isolation of the experimental variable and its impact over time • Limited in scope; can replicate • Weaknesses • Its artificiality (人為造作、人工化) • Overall, its great advantage– logical rigor (邏輯嚴謹)

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