NonExperimental designs: Developmental designs

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Non-Experimental designs Developmental designs
Small-N designs

• Psych 231 Research Methods in Psychology

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Announcements

• No labs this week work on group project data
• Journal Summary 2 due in lecture Wed
• Please write your GAs name on the checklist
• No names, SSN only

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Developmental designs

• Non-experimental or quasi-experimental
• Used to study changes in behavior that occur as a
  function of age changes

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Developmental designs

• Age serves as a quasi-independent variable
• Three major types
• Cross-sectional
• Longitudinal
• Cohort-sequential

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Developmental designs

• Cross-sectional design
• Study groups of individuals of different ages at
  the same time
• Group means are then compared

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Developmental designs

• Cross-sectional design
• Groups are pre-defined on the basis of a
  pre-existing variable
• Use age to assign participants to group
• Age is subject variable treated as a
  between-subjects variable

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Developmental designs

• Cross-sectional design
• Advantages
• Can gather data about different groups (i.e.,
  ages) at the same time
• Participants are not required to commit for an
  extended period of time

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Developmental designs

• Cross-sectional design
• Disadvantages
• Individuals are not followed over time
• Cohort (or generation) effect individuals of
  different ages may be inherently different due to
  factors in the environment
• Example are 5 year old different from 13 year
  olds just because of age, or can factors present
  in their environment contribute to the
  differences?
• Cannot infer causality due to lack of control

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Developmental designs

• Longitudinal design
• Follow the same individual or group over time
• Repeated measurements over extended period of
  time
• Age is treated as a within-subjects variable
• Changes in dependent variable reflect changes due
  to aging process

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Developmental designs

• Longitudinal design
• Rather than comparing groups, the same
  individuals are compared to themselves at
  different times
• Changes in performance are compared on an
  individual basis and overall

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Developmental designs

• Longitudinal design
• Advantages
• Can see developmental changes clearly
• Avoid some cohort effects (participants are all
  from same generation, so changes are more likely
  to be due to aging)
• Can measure differences within individuals

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Developmental designs

• Longitudinal design
• Disadvantages
• Can be very time-consuming
• Can have cross-generational effects
• Conclusions based on members of one generation
  may not apply to other generations
• Example are individuals who grew up during WWII
  the same or different from individuals who grew
  up after?

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Developmental designs

• Longitudinal design
• Disadvantages
• Numerous threats to internal validity
• Attrition/mortality
• History
• Practice effects
• Improved performance over multiple tests may be
  due to practice taking the test
• Absence of control
• Cannot determine causality

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Developmental designs

• Cohort-sequential design
• Combines elements of cross-sectional and
  longitudinal designs
• Addresses some of the concerns raised by other
  designs
• For example, allows to evaluate the contribution
  of generation effects

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Developmental designs

• Cohort-sequential design
• Measure groups of participants as they age
• Example measure a group of 5 year olds, then the
  same group 5 years later, as well as another
  group of 5 year olds
• Age is both between and within subjects variable

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Developmental designs

• Cohort-sequential design
• Advantages
• Can measure generation effect
• Less time-consuming than longitudinal
• Disadvantages
• Still time-consuming
• Still cannot make causal claims

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Small N designs

• What are they?
• Historically, these were the typical kind of
  design used until 1920s when there was a shift
  to using larger sample sizes
• Even today, in some sub-areas, using small N
  designs is common place
• (e.g., psychophysics, clinical settings,
  expertise, etc.)

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Small N designs

• One or a few participants
• Data are not analyzed statistically rather rely
  on visual interpretation of the data
• Observations begin in the absence of treatment
  (BASELINE)
• Then treatment is implemented and changes in
  frequency, magnitude, or intensity of behavior
  are recorded

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Small N designs

• Baseline experiments the basic idea is to show
• when the IV occurs, you get the effect
• when the IV doesnt occur, you dont get the
  effect (reversibility)
• Before introducing treatment (IV), baseline needs
  to be stable
• Measure level and trend

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Small N designs

• Level how frequent (how intense) is behavior?
• Are all the data points high or low?
• Trend does behavior seem to increase (or
  decrease)
• Are data points flat or on a slope?

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ABA design

• ABA design (baseline, treatment, baseline)

• The reversibility is necessary, otherwise
• something else may have caused the effect
• other than the IV (e.g., history, maturation,
  etc.)

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Small N designs

• Advantages
• Focus on individual performance, not fooled by
  group averaging effects
• Focus is on big effects (small effects typically
  cant be seen without using large groups)
• Avoid some ethical problems e.g., with
  non-treatments
• Allows to look at unusual (and rare) types of
  subjects (e.g., case studies of amnesics, experts
  vs. novices)
• Often used to supplement large N studies, with
  more observations on fewer subjects

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Small N designs

• Disadvantages
• Effects may be small relative to variability of
  situation so NEED more observation
• Some effects are by definition between subjects
• Treatment leads to a lasting change, so you dont
  get reversals
• Difficult to determine how generalizable the
  effects are

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Small N designs

• Some researchers have argued that Small N designs
  are the best way to go.
• The goal of psychology is to describe behavior of
  an individual
• Looking at data collapsed over groups looks in
  the wrong place
• Need to look at the data at the level of the
  individual

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Next time

• Statistics (Chapter 14)
• Journal summary due Wed in lecture
• Put your SSN on checklist the name of your GA
• No labs this week