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Messinger
Overview
Defining development Studying development
– Longitudinal & cross-sectional designs Study design
– Experimental, observational, and qualitative studies
Predicted variables– typically behavior and/or physiologic activity
Messinger
Development defined
Individual change that is, normative, non-reversible, relatively stable, and sequential.
Messinger
Development defined defined
Normative process – everyone’s doing it
non-reversible– reorganization of the entire person
relatively stable– you can’t go back,
sequential change– crawl before you walk
Examples
Messinger
Is development
Increasing functionality in all things?– Loss of perceptual acuity in non-native languages– Old-age
Headed toward a goal?– Development has normative outcomes, – but time goes forward– prior events cause subsequent events
not the opposite
Messinger
Overview
Studying development – Longitudinal and cross-sectional
Studying behavior– Experimental and observational
Studying outcomes– Behavior and physiology
Relate to your article reviews and final projects
Messinger
Longitudinal
Same infants over time Pro: Answers ‘How do
individuals change in time?’
Con: Takes a long time– Attrition
Final project examples?
1 2 3Ba
yley
Cog
nitiv
e Sco
re
50
60
70
80
90
100
110
120
YearM = 93.5n = 200
YearsM = 79.1n = 190
YearsM = 82.1n = 132
Typical Trajectory:Cognitive Scores Decline
Messinger
Cross-sectional
Different infants at different times
Pro: Efficient, large numbers of subjects
Con: Differences do not necessarily reflect individual’s development
– e.g. cohort
Final project examples?
50
55
60
65
70
75
80
85
90
95
DifferentIndividuals
OneYearTwoYearThreeYear
Messinger
Longitudinal vs. cross-sectional
Development is relatively stable on large time scales– Motor, physical, emotional,
communicative But choppy on smaller scales
– Only longitudinal research can show this
Emergent order from chaotic, dynamic systems
Previous example?
Messinger
Complementary, not exclusive
A single study can combine longitudinal and cross-sectional methods
Some infant studies use neither method– They look at behavior at one point in time
E.g., Neonate study
Messinger
Predictor and predicted variables
In developmental studies, – age is a predictor– behavior or physiology are predicted
Experimental and observational studies
Messinger
Stability and continuity
Stability– Rank of individual in group is stable
Continuity– Level of behavior is continuous across ages
Messinger
Experiments are unique because
They can demonstrate causality How?
Estimated Marginal Means of MEASURE_1
SMILES
321
Est
imat
ed
Ma
rgin
al M
ean
s
.16
.14
.12
.10
.08
.06
.04
.02
EXP2
Comparison
Exposed
Messinger
Experimental design
Between subject– A treatment (independent variable) is
assigned randomly– creating treatment and control groups
Within-subject– All infants get treatment and control– Examples
Rating study, Face-to-face still-face
Estimated Marginal Means of MEASURE_1
SMILES
321
Est
imat
ed M
arg
ina
l Mea
ns
.16
.14
.12
.10
.08
.06
.04
.02
EXP2
Comparison
Exposed
Messinger
Constrained behavior in experiments Gazes at stimulus
– habituation and paired preference designs Sucking & leg kicks
– Response contingencies
Messinger
Types of observational research
Quasi-experimental – differences in naturally occurring groups
Observational - – Differences in naturally occurring conditions
Complementary, not exclusive
Is age (development) studied experimentally or observationally?
Messinger
Observational
Quasi-experiment – Between subject exploration of
differences in naturally occurring groups
Drug exposure, breast-feeding, and attachment groups
Observational– Differences in naturally
occurring conditions Gazing at mother versus gazing
away
Figure 2b.
Solo Open Mouth Smiling by Gazing at Mother
Pro
port
ion
of O
pen
Mou
th S
mili
ng O
nly
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Messinger
Predicted or dependent variables
Experimental and all observational approaches measures variables
Variable - a measurable component of behavior or physiological functioning that can take on different values
Not all aspects of behavior or physiology by specific feature of interest
Messinger
Qualitative methods
Intensive description in regular language– Not measuring variables
E.g., baby biography, one infant described over time
Pro: Insight into individual and developmental process– Emerged with romantic emphasis on individual
Con: Not generalizable Complementary, not exclusive
– Role in empirical project
Messinger
Which is best?
Longitudinal or cross-sectional Experimental, observational, or qualitative?
Messinger
Observing behavior
Observed on-line or video-recorded Measured with
– Trait rating - global judgement– Time sampling– Event sampling (frequency)– Event sampling (duration)
Messinger
Physiological measures
Heart rate & respiration (video)– avoidant infants, infants on visual cliff
Electroencephalogram– Relative lateral activation during crying
Actigraphy– Index of ADD?
Increasingly important supplement to behavioral measures
Messinger
Adequacy of measures
Reliability– Consistency of measurement
Inter-rater reliability of observations
Bias– Systematic impact of unmeasured variables
Blinding in drug studies Keeping observations independent
Messinger
Validity
Are we measuring what we think we’re measuring, – Do the variables measured the constructs
mentioned in the research questions?– There is no final answer
Reunion behavior = Attachment? Smiling = Joy? Looking = Preference? Heart rate = Arousal?