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7/27/2019 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
156641049320492383919113221999595168165227195482234765122923
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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