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研究設計 Research Design. Emily Lin, PhD. (林永芬) Department of Communication Disorders University of Canterbury Christchurch, New Zealand Taiwan Academy of Physical Medicine and Rehabilitation Conference: Current Intervention for Children with Developmental Delay Taoyuan, Taiwan

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research design

研究設計Research Design

Emily Lin, PhD. (林永芬)

Department of Communication Disorders

University of Canterbury

Christchurch, New Zealand

Taiwan Academy of Physical Medicine and Rehabilitation Conference: Current Intervention for Children with Developmental Delay

Taoyuan, Taiwan

December 2, 2006

slide2

Outline

  • Basic Concepts
  • Experimental Research
    • Group Design
    • Single-Subject Design

E. Lin

what is research
What is Research?

“Research is the process of investigating

scientific questions.”

  • To satisfy the need to:
  • 1. explain events
  • 2. solve practical problems
  • 3. demonstrate certain effects
  • legal, social, professional, and scientific considerations
  • (Hegde, 2003)

E. Lin

research process
Research Process
  • Phase I: Identify the research question
    • define the research problem
    • review literature; provide theoretical framework
    • identify target population
    • identify variables
    • state research rationale
    • clarify objectives
    • state specific purposes or hypotheses
  • Phase II: Design the study(i.e., design protocol, select a sample)
  • Phase III: Methods(i.e., collect data, reduce data)
  • Phase IV: Data Analysis(i.e., analyze data, provide interpretation)
  • Phase V: Communication(i.e., report findings, suggest future studies)

(Portney & Watkins, 2000)

E. Lin

purpose of research
Purpose of Research

To determine the relationship between

variables*

  • *Some basic terms:
  • 1. constant (常數)
  • 2. variable (變數):
  • -independent variable
  • -dependent variable
  • -extraneous variable

E. Lin

slide6

Types of Research

Descriptive

Exploratory

Experimental

(Describe population)

(Find relationships)

(Cause and effect)

  • e.g.,
  • Experimental
  • (randomized
  • controlled)
  • Quasi-
  • experimental
  • Sequential
  • clinical trial
  • Single-subject
  • designs
  • e.g.,
  • Case study
  • Developmental
  • research
  • Normative
  • research
  • Qualitative
  • research
  • Correlational
  • research

(Portney & Watkins, 2000)

E. Lin

what is an experiment
What is an experiment (實驗)?
  • Manipulation of variables:

Independent variables are manipulated through:

-administration of treatment, or

-deliberate operation imposing predetermined experimental conditions combined with classification (Quasi-experiment)

  • Random selection/assignment:
    • Obtain a representative sample
    • Establish equivalency between comparison groups

E. Lin

selecting a study sample
Selecting a Study Sample

Target population (reference population)

Accessible population (experimental population)

Subject selection

Non-participants

Participants (Study sample)

Group assignment

Experimental

group

Control group

(comparison groups)

(Portney & Watkins, 2000)

E. Lin

sampling strategy
Sampling Strategy
  • Probability sampling:
    • Simple random sampling
    • Systematic sampling
    • Stratified random sampling
    • Disproportional sampling
    • Cluster sampling
  • Nonprobability sampling:
    • Convenience sampling
    • Quota sampling
    • Purposive sampling
    • Snowball sampling

(Portney & Watkins, 2000)

E. Lin

slide10

Compensations for Lack of Random Sampling

  • Homogeneous groups
    • Matching
    • Control
  • Build in extraneous factors
    • Blocking

E. Lin

validity
Validity (效度)
  • Internal validity:

the degree a cause-and-effect inference can be made based on the observed relationship between the variables

“Measure what is claimed to be measured”

  • External validity:generalization

“Generalize to other situations”

E. Lin

threats to internal validity
Threats to Internal Validity

Potential for confounding factors to interfere

with the relationship between the independent

and dependent variables:

e.g.,

  • History
  • Maturation
  • Mortality/attrition
  • Testing or test-practice effects
  • Statistical regression
  • Differential selection of subjects
  • Instrumentation

(Schiavetti & Metz, 1997)

E. Lin

threats to external validity
Threats to External Validity

Factors limiting “the degree to which

internally valid results can be generalized”:

e.g.

  • Subject selection
  • Reactive or interactive effects of pretesting
  • Reactive arrangement (Hawthorne effect)
  • Multiple-treatment interference

(Schiavetti & Metz, 1997)

E. Lin

measurement
Measurement
  • Purpose: to provide a mechanism for achieving a degree of precision in the understanding of the characteristics of the object of interest
  • Key elements:
      • Construct
      • Rules
  • Evaluation of a measurement:

1. validity (效度): measuring what was intended

2. reliability (信度): yielding consistent results

E. Lin

level of measurement
Level of Measurement

With absolute zero

Equal intervals

Ranking

Category

E. Lin

test validity
Test Validity

1. Face validity:appears to test what is supposed to test.

2. Content validity:consists of items that adequately sample the content that defines the variable being measured.

3. Criterion-related validity:yields outcomes that can be used as a substitute measure for an established gold standard criterion test.

  • Concurrent validity
  • Predictive validity

4. Construct validity:the degree the test measures an abstract construct

E. Lin

threats to test validity
Threats to Test Validity
  • Length effect: e.g., fatigue, learning
  • Enabling behaviors required of the test taker
  • The representativeness of the norm
  • Bias
  • Reliability:e.g., test-retest, inter-judge

E. Lin

slide18

Reliability

1. Test-retest reliability:

  • Repeat the whole test or a portion of test
  • Conduct a parallel test
  • Split-half method (internal consistency)

2. Inter and intra-judge reliability:

  • Total reliability
  • Trial-by-trial (point-by-point) reliability
  • Occurrence reliability
  • Nonoccurrence reliability

E. Lin

slide19

Three Basic Measurements In Descriptive Statistics

  • Central tendency: the average (“center”) score

of a distribution; mean, median, mode

  • Variability: the dispersion of scores;

range, standard deviation (SD)

3. Relative position: a score’s position within

a distribution; percentile, z-score

E. Lin

slide20

Inferential Statistics

Sample Population

Known Unknown

*Difference between subjective inference and statistical inference:

Statistical inference requires objective criteria to make decisions.

  • Inferential statistics:
  • Decision-making process
  • To estimate population characteristics from sample data
  • Assumptions made about how well the sample represents
  • the larger population. The assumptions are based on
  • two concepts of statistical reasoning:
    • Probability
    • Sampling error

E. Lin

slide21

Hypothesis Testing

  • Null hypothesis (statistical hypothesis; H0):
  • the group difference is due to sampling error
  • Alternative hypothesis (research/scientific hypothesis;
  • H1): the research hypothesis is correct
  • The purpose of posing a research hypothesis:
  • usually with the intention to reject the null hypothesis

E. Lin

slide22

Hypothesis Testing: Type I and II errors

(Real Situation )

H0 is true

H0 is false

Reject H0

Type I error

(a)

Correct decision

(1-b)

(Power of test)

(Decision)

Accept H0

Correct decision

(1-a)

Type II error

(b)

a : significance level

Power (1-b):the probability that a test will produce a significant difference at a given significance level

Type I error: The error that results when null hypothesis is falsely rejected.

Type II error: The error that results when null hypothesis is falsely accepted.

E. Lin

slide23

Hypothesis Testing

(Portney & Watkins, 2000)

E. Lin

slide24

Group Design

  • One-shot case study
  • One-group pretest-posttest design
  • Static-group comparisons
  • Pretest-posttest control group design
  • Posttest-only control group design
  • Solomon four-group design
  • Multigroup pretest-posttest design
  • Multigroup posttest-only design

E. Lin

slide25

Group Design -continued

  • Factorial designs
  • Single-group time-series design
  • Multiple-group time-series design
  • One-group single-treatment counter-balanced
  • design
  • Crossover design
  • Correlational analysis

E. Lin

slide26

Group Design: One-Way Design for Independent Groups

A1

A2

A3

S1

10

S11

10

S21

10

S2

S3

S4

S5

S6

S7

S8

S9

S10

S12

S13

S14

S15

S16

S17

S18

S19

S20

S22

S23

S24

S25

S26

S27

S28

S29

S30

Analysis Method:One-way ANOVA

E. Lin

slide27

Group Design: One-way Within-Subjects Design

A1

A2

A3

10

10

10

S1

S2

S3

S4

S5

S6

S7

S8

S9

S10

S1

S2

S3

S4

S5

S6

S7

S8

S9

S10

S1

S2

S3

S4

S5

S6

S7

S8

S9

S10

Analysis Method:One-way Repeated Measures ANOVA

E. Lin

slide28

Two-way Factorial Design

Factors:

-Factor A (teaching method): 2 levels (oral vs. visual)

-Factor B (gender): 2 levels (female vs. male)

This is a two-by-two (2X2) design.

A1

A2

S1

S2

S3

S4

S5

5

S11

S12

S13

S14

S15

5

B1

5

5

S6

S7

S8

S9

S10

S16

S17

S18

S19

S20

B2

E. Lin

slide29

Main Effect

Effect of Factor A (Teaching method)

A1

A2

5

5

S1

S2

S3

S4

S5

S11

S12

S13

S14

S15

B1

5

5

S6

S7

S8

S9

S10

S16

S17

S18

S19

S20

B2

E. Lin

slide30

Main Effect

Effect of Factor B (Gender)

A1

A2

5

5

S1

S2

S3

S4

S5

S11

S12

S13

S14

S15

B1

5

5

S6

S7

S8

S9

S10

S16

S17

S18

S19

S20

B2

E. Lin

slide31

Interaction Effect

Effect of Interaction between Factors A and B

A1

A2

5

5

S1

S2

S3

S4

S5

S11

S12

S13

S14

S15

B1

5

5

S6

S7

S8

S9

S10

S16

S17

S18

S19

S20

B2

E. Lin

slide33

Single-Subject Design

  • Synonym:
      • Single-case design
      • Single-system design
      • Time series experimentation
  • Definition: an experimental design involving the systematic collection of repeated measurements of a behavioural response over time, usually at frequent and regular intervals

E. Lin

slide34

Single-Subject Design: Length of Phases

Two choices:

        • Equal phase lengths: preset a short period time to minimize maturation, motivational changes over prolonged periods
        • Unequal phase lengths: extend baseline or intervention phases until stability is achieved

E. Lin

slide35

Single-Subject Design: Structure

      • Repeated measurement
      • Two design phases:
        • Baseline phase: period prior to treatment
        • Intervention phase: Period during treatment.

(Portney & Watkins, 2000)

E. Lin

slide36

Single-Subject Design: Assumption

Baseline data reflect the ongoing effects of background

variables, such as daily activities, other treatments, and

personal characteristics, on the target behaviours.

Therefore, when treatment is initiated, changes from

baseline to the intervention phase should be attributable to

intervention.

(Portney & Watkins, 2000)

E. Lin

slide37

Single-Subject Design: Length of Phases

Why not 1 or 2 sessions only?

        • Stability: a minimum of 3 to 4 data points in each phase (the greater the number of data points, the more obvious trends will become)

Why not 100 sessions?

        • Efficiency: also to avoid maturation, history, and other confounding factors.

(Portney & Watkins, 2000)

E. Lin

slide38

Single-Subject Design: Measuring the Target Behaviour

        • Frequency: the number of occurrence of a certain behaviour within a fixed time interval or a fixed number of trials
        • Duration: how long the target behaviour lasts
        • Magnitude: some form of instrumentation that provides a quantitative score

E. Lin

slide39

Single-Subject Design

  • Why use it?
      • Practical:fewer subjects are required.
      • Emphasis on individual performance:allowing for differentiation between subjects who respond favourably to treatment from those who are not affected by treatment.

E. Lin

slide40

Types of Single-Subject Design

        • Withdrawal design
          • A-B-A design
          • A-B-A-B design
        • Multiple treatment designs
          • A-B-C-B design
          • Interactive design: A-B-BC-B-BC
          • Alternating treatment design
        • Multiple baseline designs

E. Lin

slide41

Withdrawal Design: A-B-A Design

(Portney & Watkins, 2000)

E. Lin

slide42

Withdrawal Design: A-B-A-B Design

(Portney & Watkins, 2000)

E. Lin

slide43

Multiple Treatment Design:

  • A-B-C-B Design

(Portney & Watkins, 2000)

E. Lin

slide44

Interactive Design:

  • A-B-BC-B-BC Design

(Portney & Watkins, 2000)

E. Lin

slide45

Alternating Treatment Design

(Portney & Watkins, 2000)

E. Lin

slide46

Multiple Baseline Designs

          • Multiple baseline design across subjects
          • Multiple baseline design across conditions
          • Multiple baseline design across behaviours

(Portney & Watkins, 2000)

E. Lin

slide47

Split-Half

Method

(Portney & Watkins, 2000)

E. Lin

slide48

Split-Half Method (continued)

(Portney & Watkins, 2000)

E. Lin

slide49

Two Standard Deviation Method

(Portney & Watkins, 2000)

E. Lin

slide50

References

Hegde, M. N. (2003). Clinical Research in Communicative Disorders:

Principles and Strategies (3rd Edition).Austin, TX: Pro-ed.

Jadad, A. (1998). Randomised Controlled Trials. London: BMJ Books.

Portney, L. G. & Watkins, M. P. (2000). Foundations of Clinical

Research: Application to Practice (2nd Edition). Upper Saddle

River, NJ: Prentice Hall Health.

Schiavetti N., & Metz, D. (2002). Evaluating Research in Communicative

Disorders (4th Edition). Sydney: Allyn & Bacon.

E. Lin