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Chapter 4

PSYCH257 Chapter Notes - Chapter 4: External Validity, The Control Group, Internal Validity

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Uzma Rehman

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Chapter 4: Research Methods
Considerations in Research Design
*Balancing internal vs. external validity
*Internal validity – Confidence that effects are due to the independent variable
*External validity – Extent to which the findings are generalizable
*Ways to increase internal validity by minimizing confounds
*Use of control groups
*Use of random assignment procedures
*Use of analogue models
*Relation between internal and external validity
Different types of research designs
The Case Study
Factors That Can Limit a Pearsons Correlation Coefficient ( r )
*Homogenous group
*Unreliable measurement instrument
*Nonlinear relationship
*Ceiling or Floor with measurement
Ceiling or Floor Effect
Interpreting Correlations
*Why it is not possible to infer causality from a correlation?
1. Directionality
*Statistical attempt to overcome the directionality problem: cross-lagged panel
*Take two sets of correlations separated by a time interval
Interpreting Correlations contd.
2. Third-variable Problem:
- What is it?
/ \
v v
X <----> Y
- Statistical attempt to overcome the 3rd variable problem: partial correlations
The Experimental Method
*An experiment is a research procedure in which a variable is manipulated and the
manipulation’s effect on another variable is observed
*Manipulated variable = independent variable
*Variable being observed = dependent variable
*Allows researchers to ask such questions as: Does therapy X reduce symptoms of
disorder Y?
*Causal relationships can only be determined through experiments
*Researchers must eliminate all confounds – those variables other than the
independent variable that may also be affecting the dependent variable
*Guard against confounds:
*The control group
*Random assignment
*To avoid bias by the participant, experimenters employ a “blind design,” in which
participants are kept from knowing what condition of the study (experimental or
control) they are in
*One strategy for this is providing a placebo – something that looks or tastes
like real therapy but has no key ingredient
*To avoid bias by the experimenter, experimenters employ a “double-blind design,”
in which both experimenters and participants are kept from knowing what
condition of the study participants are in
*Often used in medication trials
Alternative Experimental Designs
*Clinical researchers often must settle for designs that are less than ideal and include:
*Quasi-experimental designs
*Natural experiments
*Analogue experiments
*Single-subject experiments
Experimental control is demonstrated within
the individual
*Evaluate behavioral data series for each individual, NOT the mean of all
Other Variations of the ABA design
BAB design
*Start with treatment, remove, return to treatment phase
*Useful when an intervention is immediately needed
ABCB design
*Multiple treatments (B & C)
*Useful when comparing interventions or IVs
*May be implemented with return to baseline in between conditions: ABAC
*May produce sequence effect (need to counterbalance)