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Validity Reliability Control

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... test administered to the same (or similar) sample on two different occasions ... Single test administered to a sample on one occasion ... – PowerPoint PPT presentation

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Title: Validity Reliability Control


1
ValidityReliabilityControl
2
Establishing Cause and Effect
  • Temporal Precedence
  • Cause has to happen before the effect
  • Covariation of Cause and Effect
  • Show there is a relationship between X and Y
  • No Plausible Alternative Explanations
  • Any other cause that can bring about the effect

3
Establishing Cause and Effect
4
Validity and Reliability
  • Measure-Related Concerns
  • Construct Validity
  • Are you measuring what you think youre
    measuring?
  • Reliability
  • Is your measure consistent in its evaluation of
    the same individuals?

5
Types of ReliabilityInter-rater reliability
  • Assesses the degree to which different
    raters/observers give consistent estimates of the
    same phenomenon
  • agreement
  • Correlation between observers scores

6
Types of ReliabilityTest-retest
  • Correlation between two observations (i.e., set
    of scores) on the same test administered to the
    same (or similar) sample on two different
    occasions
  • Assumes no change in construct being measured
  • Time between observations is crucial

7
Types of ReliabilityParallel-forms
  • Correlation between two observations (i.e., set
    of scores) on parallel forms of a test
    administered to the same sample
  • Requires generation of many items that measure
    the same construct
  • Two forms of test can be used independently
  • Assumes randomly divided halves are equivalent

8
Types of ReliabilityInternal consistency
  • Single test administered to a sample on one
    occasion
  • Assesses the consistency of the results for
    different items for the same construct within the
    measure
  • Average inter-item correlation
  • Average item-total correlation
  • Split-half reliability
  • Cronbachs Alpha

9
Relationship between reliability and validity
10
Validity and Reliability
  • Method-Related Concerns
  • Internal Validity
  • Is the independent variable the only possible
    explanation of the results shown?
  • External Validity
  • How far can the study generalize?

11
Validity
  • Internal Validity
  • Is the independent variable the only possible
    explanation of the results shown?
  • Protecting internal validity allows us to
    eliminate potential alternative explanations for
    the outcome of an experiment
  • Extraneous variables
  • Influence the DV without your intent or consent!

12
Experimental Control
  • Extraneous Variables
  • Nuisance variables
  • Make the effects of the IV more difficult to
    determine by affecting variation within groups
  • Participant characteristics
  • Unintended influences of experimental situation

13
Experimental Control
  • Extraneous Variables
  • Confounding variables
  • Vary systematically with the IV
  • Influence the difference between groups
  • The differences observed between groups could be
    attributed to the IV or the confound

14
Experimental Control
  • Extraneous Variables
  • Experimenters
  • Physiological differences
  • Rosenthal effects

15
Experimental Control
  • Extraneous Variables
  • Participants
  • Demand characteristics
  • Good participant effect
  • Response biases

16
Internal Validity
  • Exercise control to protect internal validity
    before the experiment is conducted
  • Random Assignment
  • Elimination
  • Constancy
  • Counterbalancing
  • Single- and Double-blind Experiments
  • Altering Response Sets

17
Basic Control Techniques
  • Randomization
  • Individuals have an equal chance of being
    assigned to any group in the experiment
  • Allows us to assume groups are roughly equivalent
    before administering the IV

18
Basic Control Techniques
  • Elimination
  • Extraneous variables are completely removed from
    the experiment

19
Basic Control Techniques
  • Constancy
  • An extraneous variable is reduced to a single
    value experienced by all participants
  • Standard control technique
  • Hold environment, temperature, lighting constant

20
Basic Control Techniques
  • Balancing and Counterbalancing
  • Balancing
  • Achieves group equality by distributing
    extraneous variables to all groups
  • Counterbalancing
  • Controls order effects by presenting treatments
    in a different sequence
  • Order or sequence effects
  • Carryover effects
  • Differential carryover

21
Basic Control Techniques
  • Within-Subject Counterbalancing
  • Within-Group Counterbalancing
  • Each treatment must be presented to each
    participant an equal number of times
  • Each treatment must occur an equal number of
    times at each testing session
  • Each treatment must precede and follow each of
    the other treatments an equal number of times

22
The Cola Wars!
  • Participant 1
  • Participant 2
  • Participant 3
  • Participant 4
  • Participant 5
  • Participant 6
  • P C
  • P C
  • P C
  • C P
  • C P
  • C P

23
The Cola Wars!
  • Participant 1
  • Participant 2
  • Participant 3
  • Participant 4
  • Participant 5
  • Participant 6
  • P C DP
  • P DP C
  • C P DP
  • C DP P
  • DP P C
  • DP C P

24
Basic Control Techniques
  • Single- and Double-Blind Experiments
  • The experimenter (single-blind) or both the
    experimenter and participants (double-blind) are
    unaware of the participants condition

25
Basic Control Techniques
  • Altering response sets
  • Rewrite survey items so that some negative
    responses indicate agreement and some positive
    responses indicate disagreement
  • Check for socially desirable responses in your
    survey and/or potentially undesirable cues

26
Internal Validity
  • Exercise control to protect internal validity
    before the experiment is conducted
  • Assess the internal validity of the experiment
    afterward

27
Threats to Internal Validity
  • History
  • Significant events occur between measurements

28
Threats to Internal Validity
  • Maturation
  • Participants change over time in the experiment

29
Threats to Internal Validity
  • Testing (Pretest Sensitization)
  • Repeated tests cause changes in DV practice
    effects

30
Threats to Internal Validity
  • Instrumentation
  • Changes in measurement due to changes in the
    measurement device (human or machine)

31
Threats to Internal Validity
  • Statistical regression
  • Extreme scores regress toward the mean
  • Difficult to maintain extreme scores over
    repeated measures

32
Threats to Internal Validity
  • Selection
  • Selecting participants into groups that were not
    equivalent before the experiment

33
Threats to Internal Validity
  • Attrition or Mortality
  • Experimental dropouts

34
Threats to Internal Validity
  • Diffusion of treatment
  • Participants in one group communicate information
    from the IV to the other group

35
Threats to Internal Validity
  • Interactions with Selection
  • Maturation
  • History
  • Instrumentation

36
How Important is Internal Validity?
  • It is the most important property of any
    experiment
  • An experiment without internal validity cannot
    have external validity
  • With no internal validity, you can have no
    confidence in your results

37
External Validity
  • How far can you generalize your results beyond
    your experiment?
  • 3 types
  • Population
  • Environmental
  • Temporal

38
Threats to External Validity
  • Testing/Treatment Interaction
  • Pretest may make reaction to the IV different
    from those not tested
  • Selection/Treatment Interaction
  • Effect is found only for a specific group of
    participants

39
Threats to External Validity
  • Reactive Arrangements
  • A la Hawthorne effects
  • Demand characteristics
  • Participant Characteristics
  • Specific animal species

40
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41
Threats to External Validity
  • Reactive Arrangements
  • A la Hawthorne effects
  • Demand characteristics
  • Participant Characteristics
  • Specific animal species
  • Experimental participant populations
  • College students
  • White male Americans

42
Is External Validity Necessary?
  • May want to find out if something can happen
  • We may be predicting from the real world to the
    lab
  • If we can show something happens in the labs
    unnatural setting, we may have more confidence in
    the phenomenon
  • We may study something without a real-world
    analogy

43
Validity
  • Measure-Related Concerns
  • Construct Validity
  • Reliability
  • Method-Related Concerns
  • Internal Validity
  • External Validity
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