How can we get the answers to our questions about development?

How can we get the answers to our questions about development?

What is age-related Change?

Evaluation of ResearchEvaluation of ResearchGoals of Aging ResearchGoals of Aging ResearchTypes of MethodsTypes of MethodsDevelopmental DesignsDevelopmental DesignsStrengths & Weaknesses of Strengths & Weaknesses of

typical designstypical designsOther methodological issuesOther methodological issues

Outline:Outline:

The Major Question inThe Major Question inAging Research:Aging Research:

Are differences we Are differences we observe attributable observe attributable to age?to age?

Two Two ApproachesApproaches

Experimental Experimental PsychologyPsychologyManipulate variables and Manipulate variables and measure effects on measure effects on dependent variables.dependent variables.(Individual differences are (Individual differences are noise)noise)

Differential Differential PsychologyPsychologyLooks at relationships Looks at relationships among individual among individual differences measured on differences measured on psychological variables.psychological variables.(Individual differences (Individual differences object of study)object of study)

ExperimentalExperimental:Look for interactions between age (as an independent variable) and other manipulated independent variables.(Deals with means)

Be

hav

ior

Young

Old

Level 1 Level 2 Other Variable

DifferentialDifferential: Account forage-related variance on somepsychological variable by individual differences on some other variable.(Deals with variance)

Age

BehaviorOtherVariable

a

b

e.g., b / a+b

How do we evaluate How do we evaluate research?research?

Statistical Statistical SignificanceSignificance

ReliabilityReliabilityInternal Validity Internal Validity

(control)(control)

External ValidityExternal Validity (generalizability)(generalizability)

IndependentVariable

DependentVariable

Dependent variable = f ( Independent variable )

IndependentVariable

DependentVariable

OtherVariable

OtherVariable

Age Behavior

Generalizability

Age Behavior

IndependentVariable

DependentVariable

(SAMPLE)

(POPULATION)

Threats to validity: Threats to validity: SelectionSelection

An example:An example:

Young = College Young = College StudentsStudents

Old = Nursing Home Old = Nursing Home ResidentsResidents

Threats to validity: Threats to validity: SelectionSelection

Internal ValidityInternal Validity LOWLOW because don’t differ in just because don’t differ in just

ageage

External ValidityExternal Validity LOWLOW because groups are not because groups are not

representativerepresentative

Threats to Validity: Threats to Validity: MatchingMatching

Young Middle-aged Old

Excellent

Poor

HEALTHSTATUS

AGE

MATCHEDGROUP

Research Research DesignsDesigns

AGE DIFFERENCESAGE DIFFERENCES Comparisons of different people Comparisons of different people

at different ages.at different ages.

AGE CHANGESAGE CHANGES Comparisons of the same people Comparisons of the same people

at different points in time.at different points in time.

1940 1950 1960 1970 1980 1990 2000 2010 2020

HISTORICAL TIME

70

60

50

40

30

20

10

0

CH

RO

NO

LO

GIC

AL

AG

E

Age, Cohort, & Age, Cohort, & Time of Time of

measurementmeasurement

1940 1950 1960 1970 1980 1990 2000 2010 2020

HISTORICAL TIME

70

60

50

40

30

20

10

0

CH

RO

NO

LO

GIC

AL

AG

E

Cross-sectional Cross-sectional (Differences)(Differences)

1940 1950 1960 1970 1980 1990 2000 2010 2020

HISTORICAL TIME

70

60

50

40

30

20

10

0

CH

RO

NO

LO

GIC

AL

AG

E

Longitudinal Longitudinal ChangesChanges

1940 1950 1960 1970 1980 1990 2000 2010 2020

HISTORICAL TIME

70

60

50

40

30

20

10

0

CH

RO

NO

LO

GIC

AL

AG

E

Time Lag DesignTime Lag Design

1940 1950 1960 1970 1980 1990 2000 2010 2020

HISTORICAL TIME

70

60

50

40

30

20

10

0

CH

RO

NO

LO

GIC

AL

AG

E

Age, Cohort, & Age, Cohort, & Time of Time of

measurementmeasurementLongitudinalDesign

Time-LagDesign

CrossSectionalDesign

Cross-sectional DesignsCross-sectional Designs Age and Cohort confoundedAge and Cohort confounded

Time-Lag DesignsTime-Lag Designs Time of measurement and Cohort Time of measurement and Cohort

confoundedconfounded

Longitudinal DesignLongitudinal Design Age and Time of Measurement Age and Time of Measurement

ConfoundedConfounded

Age

He

igh

t

Longitudinal

Cross-sectional

Historical Time

He

igh

t

Time-lag

Age

He

igh

t

Longitudinal

Cross-sectional

Discrepant Results?Discrepant Results?

Repeated testingRepeated testing

Differential Differential representativenesrepresentativenesss

Differential impact Differential impact of environmental of environmental changechange

Age

Beh

avio

r Longitudinal

Cross-sectional

Sequential Sequential designs:designs:

1940Cohort

1930Cohort

1920Cohort

1980 1990 2000 Time of Measurement

Group A Group B Group C40 years 50 years 60 years

Group D Group E Group F50 years 60 years 70 years

Group G Group H Group I60 years 70 years 80 years

Cohort-sequential Cohort-sequential DesignDesign

1940Cohort

1930Cohort

1920Cohort


Group B Group CAge 50 Age 60 (Same Ss

as in B)

Group D Group EAge 50 Age 60 (Same Ss as in D)

Time-sequential Time-sequential designdesign

1940Cohort

1930Cohort

1920Cohort


Group B Age 50

Group D Group EAge 50 Age 60 (Same Ss

as in D)

Group GAge 60

Cross-sequential Cross-sequential designdesign

1940Cohort

1930Cohort

1920Cohort


Group A Group BAge 40 Age 50 (Same Ss

as in A)

Group D Group EAge 50 Age 60 (Same Ss

as in D)

Sequential designs:1940Cohort

1930Cohort

1920Cohort


Group A Group B Group C40 years 50 years 60 years

Group D Group E Group F50 years 60 years 70 years

Group G Group H Group I60 years 70 years 80 years

Discuss the advantages and disadvantages of longitudinal studies of aging.

Can we talk about age “change” when we only have cross-sectional data?

DISCUSSION TOPICS:

Longitudinal StudyLongitudinal Study

People tested are of the People tested are of the same age group.same age group.

Baseline Testing and Baseline Testing and Follow Up testing Follow Up testing

The purpose is to measure The purpose is to measure age related changes.age related changes.

Cross-Sectional Cross-Sectional StudyStudy

Comparing groups of Comparing groups of people of different ages.people of different ages.

Each person is tested Each person is tested only onceonly once

Measures age related Measures age related differencesdifferences

TermTerm DefinitionsDefinitionsInternal ValidityInternal Validity - -

extent to which an extent to which an independent independent variable determines variable determines the outcome of an the outcome of an experiment.experiment.

TermTerm DefinitionsDefinitionsThreat of SelectionThreat of Selection - -

when the procedures when the procedures used to select used to select individuals for research individuals for research resulting in extraneous resulting in extraneous differences in the differences in the groups selected for groups selected for study.study.

TermTerm DefinitionsDefinitions

Threat of HistoryThreat of History - - during the time during the time between testing an between testing an individual may individual may experience something experience something that changes their that changes their behavior.behavior.

TermTerm DefinitionsDefinitions

Threat of TestingThreat of Testing - - taking a test on one taking a test on one occasion can affect occasion can affect test performance on test performance on subsequent subsequent occasionsoccasions

Longitudinal Studies Longitudinal Studies

AdvantagesAdvantagesNo threat of selection No threat of selection or cohort effectsor cohort effectsindividuals from a individuals from a single cohort form the single cohort form the study’s participant study’s participant poolpool


AdvantagesAdvantages

Allows investigators to Allows investigators to track changes that take track changes that take place within individuals place within individuals over a long period of over a long period of time.time.



Better Better statistical statistical powerpower


DisadvantagesDisadvantagesTime ConsumingTime Consuming

History Threat/Testing ThreatHistory Threat/Testing Threat

Selective dropout - over the Selective dropout - over the course of the study individuals course of the study individuals may choose not to participate may choose not to participate for a variety of reasons.for a variety of reasons.


DisadvantagesDisadvantagesIndividuals difficult to keep up Individuals difficult to keep up

with. (Ex: relocation, with. (Ex: relocation, incarceration, death -incarceration, death -especially with studies of the especially with studies of the elderly)elderly)

Obsolescence of methodsObsolescence of methods


Disadvantages Disadvantages (cont.)(cont.)Researcher Problems -Researcher Problems -

Difficult to control all aspects of Difficult to control all aspects of testing protocoltesting protocol

Some data collectors don’t use Some data collectors don’t use correct procedurescorrect procedures

Very long term studies may have Very long term studies may have high turnover so is difficult to high turnover so is difficult to keep up with the trainingkeep up with the training


Disadvantages Disadvantages (cont.)(cont.)

Possibility of investigator’s view of Possibility of investigator’s view of problem changes problem changes

Another investigator publishes Another investigator publishes results of a similar study before results of a similar study before your investigation concludes.your investigation concludes.

Funding may be difficult to obtain, Funding may be difficult to obtain, grants are stressful and time grants are stressful and time consuming consuming

Cross Sectional Cross Sectional Studies Studies


Not as time consuming, Not as time consuming, excessive study can be excessive study can be concluded in a few months.concluded in a few months.



Free of history threat - Free of history threat - everyone only tested onceeveryone only tested once



Free of testing threat - Free of testing threat - everyone only tested onceeveryone only tested once


DisadvantagesDisadvantages

Do not allow the Do not allow the measurement of age-measurement of age-related change. They related change. They determine whether one determine whether one age group of people differs age group of people differs from another age group.from another age group.



No way to control cohort No way to control cohort effects or other extraneous effects or other extraneous factorsfactors



Threat of selectionThreat of selection

Can we talk about ageCan we talk about age “ “change” when we only change” when we only have cross-sectional have cross-sectional data? Why?data? Why?

End of Class Discussion

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How can we get the answers to our questions about development?