PSYC 412 Lecture Notes - Lecture 12: External Validity, Psychiatric Medication, Mental Disorder

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PSYC 412: Developmental Psychopathology
Jan 15th, 2018
Lecture 3:
Wrap-up from Lecture #2: Sampling
o Who am I interested in studying? What population am I interested in? Define
your sample
Inclusion criteria: Who can be here? i.e. Im only interested in girls: so
one criteria would be must be a girl
Exclusion criteria: Who do I not want to include in my sample?
o Example of profs study comparing social behavior of children with (a) anxiety
and/or depression, (b) behavioral difficulties, (c) both
Inclusion criteria:
Must be clinically referred; i.e. seeking services, its gotten bad
enough that theyre getting help
Presence of anxiety and/or depression and/or behavioral
difficulties
Between 8 and 14 years of age
Living with parent or current guardian for at least 3 months
Exclusion criteria
Kids werent taking psychiatric medication
o You have to carefully consider this: the people in your study affects
conclusions you draw and limits what you can say about your findings
Can change findings, interpretations
For example, if you only recruit girls in your sample and find
association between puberty and depressive symptoms, you
cannot say in children theres an association because we dont
know about all children, just girls
o How will you get your sample?
o In 2010, chief of statistics Canada publicly resigned because of census policy
changes
All Canadians complete short form census (survey you do every 5-7
years to get basic information about population of Canada, i.e. average
age, family size, etc.)
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20% are required to fill out a longer version of the census survey with
50 questions with more detail like level of education, income, etc.
In 2010 the government wanted to make the long form of the census
optional, until that point it was mandatory
Mr. Sheikh quits because of this: saying this plan wont work if
you make it optional
If its optional, the people who choose to complete it will be
different than those who dont: systematically excluding people
who we really care about, and the sample we end up with is no
longer representative of the entire population of Canada
In 2011 the National Household Survey response rate average was
68.6% (it was 94% in mandatory long form)
Participation rates dramatically dropped once it was made
optional
This matters because information from census data informs
policies
o Key issue in sampling: we are interested because it represents a population
Sample is group filling it out, supposed to represent population, which
is the group were really interested in
Random selection: everyone in population of interest has equal
chance of being chosen
Thats how long form of census works: everyone in Canada has
equal chance of being chosen to fill out the long form census,
and this is what makes us confident that results represent
population were interested in
Sample of convenience
Schools, clinics, etc. who are willing to participate in studies
You have to be careful when talking about findings and who
you generalize your findings to
o How you get participants shapes who you get
how shapes the who
Example: camp fairs where summer camps try to recruit families
o Random selection is very expensive and difficult so most studies rely on
samples of convenience
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o To whom do you want your results to generalize?
Sample vs. population
External validity: extent I would expect results I got to generalize to
different groups of people/external conditions
To what extent would I get these results if I did this study with
different people?
o Experimental/Study validity
Internal validity
External validity
Construct validity
PART TWO
o Questions answered by developmental psychopathologists
Epidemiology
Correlates of disorder
Who develops problems and what happens to those who have them?
Interventions
Overarching theme: how do we establish causality?
o Epidemiology:
How common is a given problem and who has this problem?
Identify rates of a problem in a population
New cases over a time period = the incidence of a disorder
All cases during a time period = the prevalence of a disorder
Sampling and measurement of disorder are
critical
for this type of
study
Epidemiologists typically use random sampling (probability sampling or
population-based sampling)
Everyone in population of interest has equal chance of being
selected to be in that sample
Sample of convenience
Sample who is readily available
How common is a given problem?
Sampling
o Need to be able to generalize to the population of
interest
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Document Summary

50 questions with more detail like level of education, income, etc. In 2010 the government wanted to make the long form of the census optional, until that point it was mandatory: mr. sheikh quits because of this: saying this plan won(cid:284)t work if you make it optional. In 2011 the national household survey response rate average was. Journalist concluded that living at home in your early 20s key risk factor for violent behavior. It is possible that living at home causes violence (a -> b) A and b, like a substance abuse problem. I. e. school attendance in depressed and non- depressed teens: matched for gender, age, ses. If you recruit a sample of kids living in poverty when they are 5, measure their conduct symptoms, and return. If you remove the intervention and see it wasn(cid:284)t the cause of the behavior change then you shouldn(cid:284)t see any behavior go back up.

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