研究設計(新)98 8 7 1

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.

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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