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Research Design

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Research Design 'The program that guides the investigator in the process of collecting, analyzing, and interpreting observations. Research Design and Causality. 3 ... – PowerPoint PPT presentation

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Title: Research Design


1
Research Design
  • The program that guides the investigator in the
    process of collecting, analyzing, and
    interpreting observations. It is a logical model
    of proof that allows the researcher to draw
    inferences concerning causal relations among the
    variables under investigation (Nachmias and
    Nachmias).

2
Research Design and Causality
  • Relationships between variables Two variables
    are related to one another (i.e. are correlated)
    if one or more values of one variable tend to be
    associated with one or more values of the other
    variable.
  • Causal relationship A relationship in which one
    variable directly causes/explains the other
    variable.

3
3 Criteria for Establishing Causality
  • X is correlated with Y
  • X precedes Y in time
  • The observed relationship between X and Y is not
    spurious
  • Spurious Relationship An observed relationship
    between X and Y is said to be spurious (or partly
    spurious) if there exists a third variable Z,
    which is both a cause of Y AND is correlated with
    X.

4
Example of Spuriousness
5
Experimental Designs
  • Select a sample
  • Randomly assign subjects into 2 or more groups.
  • Observe (measure) DV for all groups (if design
    includes pretest)
  • Introduce the stimulus (IV)
  • Observe (measure) DV for each group
  • If the change in the value of the dependent
    variable varies significantly across groups, then
    we conclude that X ? Y

6
Simple Experimental Designs
  • 2-Group Pretest - Posttest Design (Classical or
    Simple Experiment)
  • R Mexp1 X Mexp2
  • R Mcontrol1 Mcontrol2

7
Simple Experimental Designs
  • 2-Group Pretest - Posttest Design (Classical or
    Simple Experiment)
  • If two different treatments (and no pure control
    group)
  • R M1A XA M2A
  • R M1B XB M2B

8
Experimental Designs
  • Key distinguishing feature of the experimental
    design
  • Randomization (random assignment of subjects to
    groups)

9
An Example Rosenberg and McCafferty
  • Hypothesis Candidate presentation (appearance)
    is related to candidate image (and therefore vote
    choice).
  • Sample University students
  • Dependent Variable Vote Choice (simulated
    ballot)
  • Independent Variable Candidate Appearance
    (picture in campaign flyer)

10
Research Design (RM)
  • 2-group Posttest Only
  • Generally
  • R XA M1A
  • R XB M1B
  • R XA (Good/Bad picture) M1A (Vote)
  • R XB (Bad/Good picture) M1B (Vote)

11
The Independent Variable (Stimulus or
Treatment)
12
The Independent Variable (Stimulus or
Treatment)
13
Results
14
Experiments and Causality
  • Correlation?

15
Experiments and Causality
  • Correlation?
  • Comparison of two or more groups (on dependent
    variable) experiencing different levels of
    exposure to the causal (explanatory) variable
    (X). This establishes correlation.

16
Experiments and Causality
  • Temporal Precedence?

17
Experiments and Causality
  • Temporal Precedence?
  • The introduction of the independent variable
    (stimulus) is manipulated by the researcher to
    insure temporal precedence.

18
Experiments and Causality
  • Spuriousness?

19
Experiments and Causality
  • Spuriousness?
  • Random assignment insures that rival hypotheses
    are ruled out, thus eliminating the threat of
    spuriousness. (How?)

20
Simple Experimental Designs
  • 2-Group Pretest - Posttest Design (Classical or
    Simple Experiment)
  • R Mexp1 X Mexp2
  • R Mcontrol1 Mcontrol2
  • OR
  • R M1A XA M2A
  • R M1B XB M2B

21
Simple Experimental Designs
  • 2-Group Posttest Only Design
  • R X M1exp
  • R M1control
  • OR
  • R XA M1A
  • R XB M1B

22
Other Types of Experimental Designs
  • Multigroup designs more than two groups
  • Multiple Group Pretest - Posttest Design
  • Multiple Group Posttest Only Design

23
Other Types of Experimental Designs
  • Time series design
  • Multiple observations over time

24
Field Experiments
  • Experiments that occur outside the artificial
    setting of laboratory (occur in the real world)
  • Example Voter mobilization strategies

25
  • Previous Research
  • Phone contact positively related to turnout
  • Research design compare turnout rate of those
    contacted to those who were not

26
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29
Determine the following
  • Hypothesis
  • Theory
  • Research design (Table 1)

30
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31
Zilber and Niven (SSQ)
  • Table 1 2-Group Posttest Only
  • R X1(black) M1
  • R X2(A-A) M2

32
Zilber and Niven (SSQ)
  • Table 3 2X2 Factorial Design
  • R (black/liberal) M1
  • R (A-A/liberal) M2
  • R (black/conserv) M3
  • R (A-A/conserv) M4
  • To see how the effect of racial label varies as a
    function of ideology, we compare
  • M1-M2 to M3-M4

33
  • Conclusion The choice of racial labels does
    affect white attitudes toward blacks, but only
    among liberals.

34
Evaluating Research DesignsInternal Validity
  • Internal Validity - the degree to which we can be
    sure that the independent variable caused the
    dependent variable within the current sample

35
Evaluating Research DesignsInternal Validity
  • Experimental designs - randomization of
    subjects/units across values of the independent
    variable greatly reduce (eliminate?) the
    potential for spuriousness to threaten internal
    validity

36
Evaluating Research DesignsInternal Validity
  • Specific factors threatening internal validity
    (experimental or nonexperemental) include
  • History
  • Maturation
  • Experimental mortality
  • Instrumentation
  • Testing

37
Evaluating Research DesignsExternal Validity
  • External Validity - the degree to which the
    results of the analysis can be generalized beyond
    the current sample/study. Can be maximized by
  • Using subjects (units) that are representative of
    the population to which ones theory applies
  • Using a laboratory that is as close to real
    life conditions as possible
  • Field experiments

38
Nonexperimental Designs
  • Deviate in some important way(s) from true
    experimental design
  • All nonexperimental designs lack random
    assignment of subjects to groups
  • But some nonexperimental designs may lack other
    features too

39
Quasi-Experiments
  • Lack random assignment, but otherwise similar to
    a true experiment
  • Example

40
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41
Matched Pair Designs (precision matching)
  • Effort to overcome nonrandom assignment of
    subjects to treatment groups (i.e. to equalize
    the comparison groups in a research design)
  • 1. Form matched pairs pairs of subjects that
    are matched based on variable(s) known to affect
    the DV
  • 2. Assign one member of each pair to treatment
    and control groups

42
Matched Pair Designs (precision matching)
  • Example
  • The Diversification of the Federal Bench Policy
    and Process Ramifications
  • Thomas G. Walker Deborah J. Barrow
  • The Journal of Politics, Vol. 47, No. 2. (Jun.,
    1985), pp. 596-617.

43
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44
Nonexperimental Designs
  • Cross-Sectional Designs
  • No manipulation of IV by researcher
  • Observations for IV and DV recorded at the same
    time

45
Example Wine and Health
  • Hypothesis Drinking wine causes individuals to
    be healthier (esp. heart)
  • Existing studies compared the health of wine
    drinkers to the health of those who do not drink
    wine
  • Research design
  • XA (Wine drinkers) M1A (Health)
  • XB (Non-drinkers) M1B (Health)

46
Spurious Results?
47
Controlling for Affluence
  • Research design
  • XA (Affluent Wine drinkers) M1A (Health)
  • XB (Affluent Non-drinkers) M1B (Health)
  • XC (Poor Wine drinkers) M1C (Health)
  • XD (Poor Non-drinkers) M1D (Health)

48
Another (Possible?) Example
49
Stack Gundlach
  • Hypothesis There is a positive relationship
    between exposure to country music and suicide
    rates
  • Research design
  • XA (no country music) MA (suicide rate)
  • XB (1 station) MB (suicide rate)
  • XC (2 stations) MC (suicide rate)
  • XD (3 stations) MD (suicide rate)
  • Xi ( etc.) Mi (suicide
    rate)

50
Stack Gundlach
  • Findings 51 of the variation in urban white
    suicide rates can be explained by variation in
    airtime devoted to country music
  • Is this result spurious?

51
Nonexperimental Designs
  • Time Series Design repeated observations for X
    and Y for a single unit
  • Panel Time Series Design repeated observations
    for X and Y for a group

52
Nonexperimental Designs
  • Case Study
  • X O1
  • Inference made by examining one case.

53
Historical Development of Ethical Standards in
Observational Research
  • 1974 - National Research Act
  • National Commission for the Protection of Human
    Subjects of Biomedical and Behavioral Research
  • identify the basic ethical principles that should
    underlie the conduct of biomedical and behavioral
    research involving human subjects and to develop
    guidelines which should be followed to assure
    that such research is conducted in accordance
    with those principles
  • Belmont Report (1979)

54
Milgrams Obedience Experiments
  • Experiment advertised as test of memorization
    training through electric shock
  • Those being tested were actually actors
  • Lab assistants hired to administer shocks were
    the true subjects
  • 65 of lab assistants were willing to administer
    shocks of up to 450 volts

55
The Stanford Prison Experiment
  • Phillip Zimbardo, 1971
  • Goal to study the psychological effects of
    imprisonment on guards and prisoners
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