c.scientific methods 2correlationalresearch

7/21/2019 C.scientific Methods 2Correlationalresearch

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Scientific Methods II:Scientific Methods II:

CorrelationalCorrelational ResearchResearch

EXAMPLESEXAMPLES

"MARRIAGE SLOWS CANCER DEATHS"MARRIAGE SLOWS CANCER DEATHSEvidence that married people have a betterEvidence that married people have a better

chance of surviving cancer than do singleschance of surviving cancer than do singlesmeans that the unmarried might be goodmeans that the unmarried might be goodtargets for cancertargets for cancer--prevention programs.prevention programs.Married people with cancer had a 23%Married people with cancer had a 23%higher overall survival rate than thehigher overall survival rate than theunmarried.unmarried.

Example 2Example 2

Isolation increases with Internet useIsolation increases with Internet use

Psychologist Robert Kraut and hisPsychologist Robert Kraut and hiscolleagues report that greater use of thecolleagues report that greater use of theInternet leads to shrinking social supportInternet leads to shrinking social supportand happiness, and increases inand happiness, and increases indepressiondepression and lonelinessAnd theand lonelinessAnd thefindings were unexpected, Kraut says,findings were unexpected, Kraut says,given that most people use the Internet forgiven that most people use the Internet forchat lines and echat lines and e--mail, not just to isolatemail, not just to isolatethemselves in mounds of electronicthemselves in mounds of electronic

information.information.

Example 3Example 3

Revenge of the BeakerRevenge of the Beaker Bunch..ResearchersBunch..Researchers Find thatFind thatScientists Live LongerScientists Live Longer

If it were a movie, it would probably be called "If it were a movie, it would probably be called "Nerds:TheNerds:The

Ultimate Revenge. A study spanning nearly 70 yearsUltimate Revenge. A study spanning nearly 70 years

suggests that, all else being equal, scientists live longersuggests that, all else being equal, scientists live longer

than nonthan non--scientists According to Friedman's study,scientists According to Friedman's study,

nonscientists are 26 percent more likely to die at any givennonscientists are 26 percent more likely to die at any given

age than scientists. In a sample of 600 men born aroundage than scientists. In a sample of 600 men born around

1912, Friedman's group found that only 67% of non1912, Friedman's group found that only 67% of non

scientists were still alive by age 70, compared to 72% ofscientists were still alive by age 70, compared to 72% of

the scientists...the scientists...


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CorrelationalCorrelational ResearchResearch

CorrelationalCorrelational research examines whether 2research examines whether 2factors are naturally associated. [Cofactors are naturally associated. [Co--relation: therelation: the

degree to which one variable is related todegree to which one variable is related toanother.]another.]

Examples focus on naturally occurringExamples focus on naturally occurringrelationshipsrelationships

marriage & cancer recoverymarriage & cancer recovery

Internet use & depressionInternet use & depression

occupation & longevityoccupation & longevity

Correlations: The BasicsCorrelations: The Basics

Numerical range:Numerical range: --1.00 to +1.001.00 to +1.00

The Correlational Method

Correlation Coefficient

Positive correlations indicate that anincrease in one variable is associated with

an increase in the other.

Negative co rrelations indicate that an

increase in one variable is associated

with a decrease in the other.


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Surveys

The correlational method often relies on

surveys, as well as on observational data.

Surveys are used when the variable of

interest is not easily observable.

How do we evaluateHow do we evaluate correlationalcorrelational

findings?findings?

Amount use Internet is associated withAmount use Internet is associated withgreater depression. Why?greater depression. Why?

3 possible explanations3 possible explanations

Using InternetUsing Internet depressiondepression

DepressionDepression greater Internet use (cannotgreater Internet use (cannotdetermine direction of causality)determine direction of causality)

A 3A 3rdrd variable might be related to bothvariable might be related to bothusing the Internet and becomingusing the Internet and becomingdepresseddepressed


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33rdrd VariablesVariables

People.People.

People.People.

EvaluatingEvaluating CorrelationalCorrelational ResearchResearch

CorrelationalCorrelational research cannot determineresearch cannot determine

causality.causality.

Problems knowing direction of causalityProblems knowing direction of causality

Problems knowing whether some 3Problems knowing whether some 3rdrd

variable (confounding variable) mightvariable (confounding variable) might

explain the observed correlationexplain the observed correlation

How do we evaluateHow do we evaluate correlationalcorrelational

findings?findings?

Consider in context of research on TVConsider in context of research on TV

exposure and aggressionexposure and aggression

Start w/theoretical idea and to test specificStart w/theoretical idea and to test specific

hypotheses.hypotheses.

Hypothesis: Children who watch moreHypothesis: Children who watch more

violent television shows behave moreviolent television shows behave more

aggressively.aggressively.


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TV & Violent ContentTV & Violent Content

8 out of 10 Sat. morning programs contain8 out of 10 Sat. morning programs contain

violenceviolence Sat. morning childrens shows: 20 violentSat. morning childrens shows: 20 violent

acts per houracts per hour

Average American watches 4 hrs of TVAverage American watches 4 hrs of TV

per day, or over 1000 hrs. per year.per day, or over 1000 hrs. per year.

What is relationship between watching TVWhat is relationship between watching TV

and childrens aggressive behavior?and childrens aggressive behavior?

TV and AggressionTV and Aggression

Many studiesMany studies

SampleSample correlationalcorrelational paradigm:paradigm:

Parents record how much TV their kids watchParents record how much TV their kids watch

Teachers record aggressive behaviorsTeachers record aggressive behaviors

(hitting, pushing, shoving, insulting, etc.)(hitting, pushing, shoving, insulting, etc.)

IV AND DV inIV AND DV in CorrelationalCorrelational ResearchResearch

QuasiQuasi--Independent Variable: how muchIndependent Variable: how much

TV kids watch (*TV kids watch (*not*not* manipulated, but actsmanipulated, but acts

like IV)like IV)

Dependent Variable: amount ofDependent Variable: amount of

aggressive behavior at schoolaggressive behavior at school


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TV and Aggression:TV and Aggression: CorrelationalCorrelational StudiesStudies

Conclusion: Children who watch TV thatConclusion: Children who watch TV that

includes violent content are more likely toincludes violent content are more likely tobehave aggressively.behave aggressively.

Why?Why?

Theory: Watching TV causes aggressionTheory: Watching TV causes aggression

But: Maybe more aggressive kids areBut: Maybe more aggressive kids are

attracted to watching violence on TVattracted to watching violence on TV

(direction of causality)(direction of causality)

Or: A 3Or: A 3rdrd variable might account for thevariable might account for the

relationshiprelationship

Third VariablesThird Variables

What are some possible third variablesWhat are some possible third variables

that could explain the correlation betweenthat could explain the correlation between

watching TV and aggressive behavior?watching TV and aggressive behavior?


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Marriage and Surviving CancerMarriage and Surviving Cancer

Direction of causality is not as much of aDirection of causality is not as much of a

problem (unlikely that surviving cancerproblem (unlikely that surviving cancercaused marriage!)caused marriage!)

What are some 3What are some 3rdrd variables that couldvariables that could

account for the greater survival rate ofaccount for the greater survival rate of

married individuals?married individuals?

DisadvantageDisadvantage

Correlation cannot determine causalityCorrelation cannot determine causality

Even if we measure possible thirdEven if we measure possible third

variables (e.g., measure eating habits,variables (e.g., measure eating habits,

measure health care, etc.) and usemeasure health care, etc.) and use

statistical techniques to control for them,statistical techniques to control for them,

we still cannot be sure about the causewe still cannot be sure about the cause--

andand--effect relationship.effect relationship.

ThenWhy doThenWhy do correlationalcorrelational research?research?

Allows for the study of problems thatAllows for the study of problems that

would be difficult to study in the labwould be difficult to study in the lab

Cant manipulate who is married or not,Cant manipulate who is married or not,

who has a stressful job or not, gender,who has a stressful job or not, gender,

race/ethnicityrace/ethnicity

Useful for generating hypotheses that canUseful for generating hypotheses that can

be tested later in a controlled experimentbe tested later in a controlled experiment


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Video onVideo on correlationalcorrelational methodmethod

Retrospective StudyRetrospective Study

Observe some outcome (lung cancer) andObserve some outcome (lung cancer) and

then gather information from people withthen gather information from people with

and without the outcome (e.g., aboutand without the outcome (e.g., about

smoking, eating habits, exercise, parentingsmoking, eating habits, exercise, parenting

style)style)

Prospective StudyProspective Study

A sample of individuals (preferably aA sample of individuals (preferably a

representative sample) is followed overrepresentative sample) is followed over

time to see whether certain experiencestime to see whether certain experiences

predict a later outcome (e.g., whetherpredict a later outcome (e.g., whethersmoking predicts later lung cancer)smoking predicts later lung cancer)


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Common CauseCommon Cause

Kids who eat more sugar might be moreKids who eat more sugar might be more

aggressive (during sugar high) and watchaggressive (during sugar high) and watchmore TV when their blood sugar drops andmore TV when their blood sugar drops and

they become lethargic.they become lethargic.

Common cause would explain why we seeCommon cause would explain why we see

an association between TV andan association between TV and

aggressionaggression

Confounding FactorConfounding Factor

Something that occurs (accidentally) thatSomething that occurs (accidentally) that

provides an alternative explanation for theprovides an alternative explanation for the

correlation. (Video: speed limit lowered,correlation. (Video: speed limit lowered,

but confound = gas crisis and less driving)but confound = gas crisis and less driving)

CoincidenceCoincidence

Two variables are coincidentallyTwo variables are coincidentally

associated, but doesnt happen again.associated, but doesnt happen again.


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Simpsons ParadoxSimpsons Paradox

Lurking variables can change the directionLurking variables can change the direction

of an association.of an association. In video, more men than women applied toIn video, more men than women applied to

law school, and the law school had easierlaw school, and the law school had easieradmission standards than the businessadmission standards than the businessschool. Thus, the overall numbers (acrossschool. Thus, the overall numbers (acrossboth programs) appeared to show thatboth programs) appeared to show thatmore men were accepted to themore men were accepted to theprofessional programs.professional programs.

Professional Schools

Applied Accepted

Men 360 198 55%

Women 200 88 44%

*Looks like few women admitted

Business School

Men 120 18 15%

Women 120 24 20%

*Greater % women admitted than men

Law School

Men 240 180 75%

Women 80 64 80

*Greater % women admitted than men

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