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Lecture 6

PSYB30H3 Lecture Notes - Lecture 6: Berkeley, California, Twin Study, Equivalence Class


Department
Psychology
Course Code
PSYB30H3
Professor
Marc A Fournier
Lecture
6

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PSYB30H3: Personality Psychology
Lecture 6: Heritability, Continuity, & Change
Marc A. Fournier
Part I. Continuity / Coherence of Personality
Continuity of Personality
- Do individual differences in some attribute predict individual differences in that
same attribute at some later point in time? (X1 X2)
- Consistency of individual differences- i.e. relative position or rank order- within a
population of individuals over time
- Differential continuity is independent if normative changes in trait levels
Ex: height, intelligence (stable differences)
- How early in life can we see personality consistency? And where (if ever) does
personality become set in stone?
Freud by age 5 or 6 personality is set
James by age 30 personality is set like plaster (time to grow and change)
Roberts & DelVecchio (2000):
Meta-analyzed findings (averaging technique) from 152 longitudinal studies
involving a total of 3,217 consistency coefficients and 50,207 participants
Functions of 2 principles:
- Consistency increased as a function of age (the older you are the more stable you
are). Holding time interval constant at 6.7 years consistency coefficients equaled:
.31 in infancy
.43 in middle childhood
.54 during the college years
.64 one’s 30’s
.74 one’s 50’s
- Consistency decreased as a function of that time interval (more time you let pass
the more evidence/change you will see). Holding age constant at 20 years,
consistency coefficients equaled:
.55 over a 1 year period
.52 over a 5 year period
.49 over a 10 year period
.41 over a 20 year period
.25 over a 40 year period
- Differential (or rank order) continuity of traits emerges in childhood and peaks
around the age of 50 but not at a level high enough to conclude that our traits at
some point become set in stone
Coherence of Personality
- Do individual’s differences in some attribute predict individual differences in
some other attribute at some later point in time? (Y1Y2)
- Y and z are manifestations of x
- Underlying trait that remains stable over time but changes in how it is expressed
over time
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- The inferred consistency of some underlying attribute despite observed changes in
its behavioral expression
- The investigator must have a theory of how the diversity of behavior observed
across the life course can be said to belong to the same equivalence class
Berkeley Guidance Study:
A study initiated in 1928 with every third birth in Berkeley, CA (original N = 214
subjects) over a period of one and a half years
Mothers were interviewed when subjects were ages 8-10; life outcomes were
collected when subjects were ages 30 and 40
Caspi, Elder, & Bem (1987): Moving Against the World: Life-Course Patterns of
Explosive Children Frequency and Severity of Temper Tantrums in Late Childhood
Predicted
- In men (from middle-class homes) deterioration in SES, erratic work lives and
divorce
- In women- marriage to men in lower SES, divorce and inadequate parenting
Summary of Part 1
- There is considerable evidence of trait continuity across the life course
- The continuity of traits emerges early in life and peaks around 50
- Although our underlying traits are theorized to remain constant, their correlates
can vary across the life course
Part II. Methods of Behavioral Genetic Research
The Jim Twins
- Jim Springer and Jim Lewis were identical twins separated at birth, who met for
the first time at 39 years of age
- Their striking similarities in terms of personality and life outcomes raise the
intriguing question to what extent is personality genetically determined?
The Human Genome
- Genome refers to the complete set of genes that an organism possesses
- The human genome contains somewhere between 20,000 and 25,000
- Genomes are located on 23 chromosomes pairs
Heritability
- The proportions of observed variance in the group of individuals that can be
accounted for by the genetic variance
- The degree of variability is a group of people which genetics cause the differences
- .1 10% of observed variation is accounted for (low variability)
- 90% of the phenotypic variation is heritable
Misconceptions About Heritability
- Heritability estimates
Are precise (no they aren’t)
Stay the same over time (no they don’t)
Can be applied to a single person (no they cant)
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