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Lecture 7

PSY210H1 Lecture Notes - Lecture 7: Biological Determinism, Epigenetics, Phenotype

Course Code

of 11
March 7 2011
Genetics, Epigenesis, and Plasticity
Problem the developmental researchers often face
Independent variable is often a characteristic of the individual we are
o Ie, height you can’t just chop people’s feet off to alter their
o Affect of intelligence on academic success how do you alter
people’s intelligence?
For these reasons, we often have to rely on quasi-experiments
o We let nature do part of the work for us take groups that
different naturally on independent variable, ie, people with
high IQ and people with low IQ reliable correlation with
academic success
o But, self regulation is a better predictor
o can't definitively establish correlation BUT can make
plausibility argument
a lot of developmental psych research relies on these quasi-
a lot of development occurs over a long period of time, therefore
putting strains on measurement and experimentation
o ex. Attrition affect
start with a group of 100 grade 1s
by grade 5, you’ve lost half of them – they’ve moved,
gotten sick, etc.
by grade 12, you’re down to 25% - does your study still
apply? Are you still doing the same study? Do your
results still generalize?
Hard to keep people
People also change a lot over long periods of time, introducing
experimental confounds
One of the solutions to this is a longitudinal study
o Two ways you can do this
o Correlational
Consistency of behaviour across a set of measures
Experimental, aka, intervention study introduce some
manipulation of IV at one point in development and
track affect on DV through different points in
Confounding made worse by this
Attrition problem subject pool goes down
Repeated testing alters behaviour your very
attempt to test them over a long period of time
gives them lots of opportunity to figure out what
you’re trying to do and thwart your experiment
Repeating an IQ experiment every 5-6 months
gives people time to read up on IQ test in
Theoretical obsolescence
o Starting a longitudinal study based on a
theory that was hot in the 1980s by the
time you’re done, no one cares about your
theory any more anything older than
10-15 years is rendered useless, obsolete
Longitudinal studies are very expensive
o Lab space, funding, access to grad
students, measuring equipment
Cross-sectional study synchronically vs. diachronically study
different children of different ages all at once
o Avoids many of the above problems, but hard to establish ideas
of stability can’t tell how stable a characteristic is over a long
period of time
o Problem with cross-section:
Cohort affect problem with studying lots of people of
different ages at the same time is that there can be
events that affect all of them, regardless of which age
group they belong to
Shared environmental/cultural/historical factors
Studying grade 4, 6, 10, and 12 during the Great
Depression they’re all experiencing great
amounts of anxiety this trait might not be
Different problems come with different kinds of studies
Cross sequential design
o Two cross-sectional studies at two different time periods
controls for the cohort effect and attrition
Study 3 groups of people
1 2 <--progression
1 3 6
2 7 10
3 10 13
-three groups of people
o Able to compare one group of ten year olds to the other
o Best overall result but almost never done
o Very expensive to do
o Triple the cost three times the longitudinal study
o Extra layer of difficulty
o Time-consuming
Over-arching themes
o There is no important investigation without significant
theoretical controversy
o Often have to supplement with arguments
o Each design has important defects that you must argue as to
why they don’t matter to your research
o What guides these arguments? The psychological frameworks,
which are guided by the philosophical frameworks
o In able to be able to make good sense of an empirical result,
you have to be able to read it at all of those levels
Now that we know how to look at development let’s start looking at it
Knowing how is actually more important than doing it
Nature vs. nurture debate is dissolving
o How do we go about studying this?
o Sharpen up terms: nature = genetic info, biology, nurture =
o how do we go about studying the relative contributions of
genes and environment? What are we discovering?
o Best models vs. best methods
o People typically do not allow you to manipulate genes, and up
until recently, we didn’t even know how
o Reliance on quasi-experimental designs, then supplementation
with plausibility arguments
How do we go about this?
o Set of designs:
Family studies
Genotype vs. phenotype
o Genotype = interaction of phenotype and
o Phenotype = genes underlying a trait
Ex. Intelligence what are the relative
contributions of genes and the environment to
Everyone is some sort of interactionist every
single trait in you is determined by nature and
Phenotypic similarity tracks genotypic similarity