Empirical Research Designs

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    Empirical Research designs

    Experimental

    Quasi experimentalCorrelational

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    Experimental designs

    Basic exp: Control Group and Exp. Group

    Control group: DV

    Exp group : IV and DV

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    Exp designs aim at drawing causal

    inferences

    Three conditions of causal inferences

    Covariation

    Time order Non-spuriousness

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    These conditions are satisfied through three

    components of exp designs

    Comparison to determine covariation

    Manipulation to determine time order

    Control to determine non spuriousness

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    Threats to internal validity/control

    Extrinsic factors

    Groups are different from each other before enteringthe experiment

    Intrinsic factors

    History: Social, political and environmental canges

    Maturation: Biological and psychological changes thatoccur in participants

    Instrumentation: Changes in instruments

    Testing experience: Practice effect Regression artifact: Tendency to move toward average

    Reactivity: Reactions to the experimental situations

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    Types of experimental designs

    Experimental designs

    N>1

    Singlefactor

    Independentgroups

    Randomized Matched

    Repeatedmeasures

    Incomplete Complete

    Factorial

    Independentgroups

    Repeatedmeasures Mixed

    N=1

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    Independent groups/Between groups

    Randomized: Random assignment to the groups

    Block randomization. E.g there are five

    experimental conditions (12345) and 10

    participants to be in each condition You will make

    10 blocks of five conditions through random

    number tables. Like following

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    Matched: To match the groups on the

    variables that may effect DV

    Matching by frequencies

    Matching by averages

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    Both designs are used forbalancing the

    confounding variables

    To control for reactivityplacebo controland

    double blind techniques are used

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    Repeated measures/within

    group designs

    Same subjects participate in both

    experimental and control conditions

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    Reasons for using repeated measures

    designs/benefits

    1. Limited number of participants available

    2. Convenience

    3. Less error variation: no confounding due toindividual differences

    4. Requirement of the study:To study changesover time, to study how participants comparestimuli

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    PRACTICE

    CONFOUNDING FACTOR/THREAT TO

    INTERNAL VALIDITY:

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    Example of repeated measures design

    Stroop effect (Stroop, J. R., 1935)

    Two conditions

    1.Naming the colour in square patches

    2. Naming the colour in words when colour ofprint and words are different

    GREEN BLUE RED YELLOW

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    Balancing practice effects

    Complete designsEach condition is administered to each participant

    several times in different orders

    Order effects are balanced within each participant

    Incomplete designs

    Different individuals receive different orders ofconditions

    Order effect is balanced out across participants

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    Repeated measures: Complete designs

    Block randomization

    ABBA design

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    Block randomization

    Conditions of the experiment are randomly

    ordered each time they are presented

    Use

    when performance of participants can be

    affected by anticipation effects

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    Block randomization with random number table

    1566410493204923839191132219995

    95168165227195482234765122923

    For two conditions AB and 8 sets of trialsrandomly selected sequence of AB will be

    AB, BA, AB, AB, .

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    ABBA

    A random sequence o f all conditions arepresented followed by the opposite of the

    sequence

    For two conditions and eight sets of trialssequence will be

    AB, BA, AB, BA, AB, BA, AB, BA

    UseWhen it is not possible to administer

    conditions often enough to be balanced

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    Repeated measures: Incomplete designs

    With only two conditions half of the participants receive

    the AB order and other half BA order

    With more than two conditions there are two choices

    All possible orders

    for four conditions, there are 24 orders. (N!= 4X3X2X1=24)

    Selected orders

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    Selected orders (cont)

    Random starting order

    Begin with random order of conditions and

    rotate the sequence systematically with each

    condition moving one position on the left

    each time

    BACD, ACDB, CDBA, DBAC

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    Selected orders (cont.)

    Latin square

    Each condition appears at each ordinal

    position once

    Each condition precedes and follows each

    condition only once

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    How to construct Latin square

    1. Randomly order the conditions(e.g., BADC)

    Number the conditions(e.g., 1=B, 2=A, 3=D,4=C)

    For first row use rule, 1,2,N,3,N-1,4,N-2,5,N-3,6,N-7,

    and so on (BACD)

    For the second row add one to each number in first

    row and consider N=1 (2314 or ADBC)

    Add 1 to each number in previous row and considerN =1(3421 or DCAB)

    Add 1 to each number in previous row and consider

    N =1(4132 or CBDA)

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    BACD

    ADBC

    DCAB

    CBDA