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

2. 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. 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. 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. 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. 6 random assignment and random sampling

7. 7 How to randomly assign?

8. 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. 9 Matching

10. 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. 11 Types of Experimental Design Again, components of classical experimental design ( 古典實驗法的三個要素 ) :

12. 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. 13 Preexperimental Research Designs

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

15. 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. 16 Design Notation O = observation of dependent variable X = treatment (independent variable) R = random assignment Symbols in time order: from left to right O 1 = pretest, O 2 = posttest See Table 9.2 (p. 261)

17. 17 A Comparison of Various Experimental Design

18. 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. 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. 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. 21 The double-blind experiment

22. 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. 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. 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. 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 )