Research MethodsUniversity of Massachusetts Boston

©2012 William Holmes1

A B?

Correlation is not Causation

Post Hoc fallacy“For Example” is not proofBelief is not theory

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Supporting EvidenceTemporal OrderingTheoryRejection of Rival Hypotheses

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Correlation between eventsCorrelation between

characteristicsData a result of research

having internal validity (not biased research)

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Potential outcomesObserved outcomesIndividual versus average

(expected) outcomesCompleters versus non-

completersStable Unit and Treatment

Value Assignment--SUTVA

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Cause precedes effectChronological ordering—

happenstance Conceptual ordering—theory Process ordering—empirical process

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Theoretical Assumptions of Program

SocialPsychologicalEconomicBiological

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Controlling Competing Influences—confounding variables

Control by Sampling--exclusionControl by Design--randomizationControl by Statistical Procedures--

controlling

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V=ViolenceSA=Substance

AbuseD=Depression

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The rival hypotheses: violence causes depression vs. substance abuse causes depression

V=ViolenceSA=Substance

AbuseD=Depression

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Indirect effects between violence and depression

V=ViolenceSA=Substance

AbuseD=Depression

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Spurious correlationbetween violence and depression

V=ViolenceSA=Substance

AbuseD=DepressionG=Genetics

Effect is conditional on other variable

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G

History—external to experimentMaturation—developmental changeInstrumentation—biased measuresSubject-Experiment Interaction—

persons messing with the experimentTesting Effects—persons learning from

the experiment

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Level of Measurement

Measures of Association

Test of Significance

Nominal/categorical

Percentage, Odds Ratio, Logit, Phi

t, Chi-square

Mixed Percentage, Means, Eta

t, F

Interval/Ratio Correlation, Regression

t, F

Determine presence of relationship--significance test or substantive criteria

Determine strength of relationship--measure of association

Compare bivariate results with what happens when controls are introduced

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