Research Design
主講人：周桂如 教授 臺北醫學大學護理學研究所 02-27361661轉6302 E-mail: kueiru@tmu.edu.tw
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I. Selecting A Research Design -Concepts Important to Design:
1. Causality: Hume(1996) identified three conditions: • There must be a strong correlation between the proposed cause and the effect • The proposed cause must precede the effect in time • The cause has to be present whenever the effect occurs
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Others: necessary and sufficient
• The proposed cause must be necessary for the effect to occurs (the effect cannot occur unless
the cause first occurs) • The proposed cause must also be sufficient (requiring not other factors)
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Others: necessary and sufficient
Cook & Campbell (1979) • There could be no alternative explanations for why a change in one variable seemed to lead to a
change in a second variable
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2. Multicausality: a number of interrelating variables
can be involved in causing a particular effect • Necessary and sufficient do not hold up • Very few phenomena in nursing can be clearly
pinned down to a single cause and a single effect
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3. Probability: Based on multicausality: the probability that a
specific effect will occur, e.g., if A occurred, there was a 50 percent probability that B would occur
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4. Bias: how to reduce bias? Good design is one way to reduce the bias 5. 操控(Manipulation): is used in experimental and
quasi-experimental(準實驗) research and is sometimes called the "treatment”
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6. 控制(Control): having the power to direct or manipulate factors to achieve a desired outcome • Selection of subjects for the study: (隨機化) randomization, matching, control group, experimental group • Statistical control – experimental var. – extraneous var. – error var. 8
a. Based on the amount of control: (con’t)
– Level III: experimental designs • Experimental • Quasi-experimental
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a. Based on the amount of control: (con’t)
– Level II: survey designs • Comparative • Correlational
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a. Based on the amount of control: (con’t)
– Level I: exploratory-descriptive designs • Descriptive • exploratory
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Types of Research Design:
a. Based on the amount of control: 1. 實驗性研究設計 (Experimental research design):
• Provide the greatest amount of control • More closely examine causality
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Types of Research Design:
• Three essential elements of experimental research: randomization, researcher controlled manipulation, of the independent variable, and
researcher control of the of the experimental situation (a control or comparison group)
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The Experimental Method
• Mill’s Criteria: Cause and effect 1. Cause must precede the effect (in time):
If A is a cause of B, then A must occur first
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The Experimental Method
• Mill’s Criteria: Cause and effect 2. Cause and effect must be related: When A is
present, B should be present; When A is absent B should be absent: when A changes value, B should change value.
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The Experimental Method
• Mill’s Criteria: Cause and effect 3. Given A and B are related, non-causal
explanations of that relationships must be ruled out. • Internal vs External variable
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Basic experimental designs (pretest-posttest experimental design)
RE Pretest RC
Pretest
X
Post-test
R
O1 X O2
Post-test
R
O1
O2
• The most commonly used experimental design
• More than one means to measure the dependent var. is advisable-- avoid mono-operation, mono-method bias
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Basic experimental designs (pretest-posttest experimental design)
RE Pretest RC
Pretest
X
Post-test
R
O1 X O2
Post-test
R
O1
O2
• Advantage: decreases threats to internal validity: (history, maturation, testing, selection, statistical regression)
• Disadvantages: differential influence of mortality, limited generalizability of results
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Post-test only control group design
RE
X
RC
Post-test
R
Post-test
R
X
O O
• The most commonly used experimental design • More than one means to measure the dependent var. is advisable-- avoid mono-operation, monomethod bias
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Thank You! 20