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Lecture 3

01:830:271 Lecture Notes - Lecture 3: Socioeconomics, Random Assignment

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Three Basic Designs
1. Cross Sectional
Take infants of each age and compare how they can complete an activity
Pros quick to develop research, doesn’t cost much,
Cons not developmental design because you’re collecting information from each
child once; there is no change over time since you receive the information at one
time in each infant. You’re only getting an average of what tasks the infants can
complete at each age, but not seeing the development in between ages because
there is no retesting of the same infant as they grow.
Cohort Effects A group of individuals of the same age and historical experiences.
o You cannot conclude that children age 4 can complete a task better than children
age 3 because of the year gap in between them.
This is because there may have been an experience in the age 4 group that
influenced them to complete a task better.
The data you receive may be influenced by these effects. It makes results
difficult to conclude from.
o If 20 year olds can type 300 characters in a minute and 50 year olds can type 75
characters in a minute you cannot conclude that a 20-year-old will not be able
to type 300 characters when they are 50 years old.
There is no developmental change; no single person was tested over the 30
years to see if they type the same characters over time or not.
2. Longitudinal
Taking multiple measurements over the change of time. Observe the same 3 year
olds when they turn 3.5 years and 4 year olds, etc.
Pros this is developmental design because you can see the change over time. Find
out if kids are early or late bloomers; or average.
Cons takes time to analyze data, costs are more expensive because of the time it
takes to collect data. Kids are doing the same test, which can mean that the kids are
completing a task faster because they had practice.
Selective Attrition people drop out of research study.
o You start off with more participants than you end up with. Recruit 120 if you need
100 results because people end up leaving the research.
o Individuals who drop out may have had a different result that may be meaningful
that may have caused them to drop out.
Data is not “randomized” or full of all kinds of ethnic kids, so the data results
cannot be applied to all kids when you reach a conclusion.
Kids that are living in underclass socioeconomics are more likely to drop out.
Kids that are sick or likely to be hospitalized are more likely to drop out
because of inconvenience.
o Kids living in lower class status housings are less likely to have experience with
the certain task being tested vs. the kids who live in upper class households that
are more likely to have access to toys.
3. Sequential (Cross-Sequential)
A combination of cross-sectional and longitudinal
Start off with multiple groups of cohorts, you test those individuals repeatedly over
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