Post on 05-Mar-2021
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EXPERIMENTAL METHODS
Experimental Designs• Experiments – examining behavior in a _______ lab setting
• Always approached __________: Describing behavior using numbers
• Controlled lab setting separates experiments from non-experiments• Allows experimenter to
know exactly what’s causing behavior
Experiments Uncover Causation• Experiments try to control everything that affects participants• Making sure all participants have the same experience
• Same room
• Same temperature / lighting
• Same materials
• Same experimenter
• Same confederate(s)
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Experiments Uncover Causation• Experiments try to control everything that affects participants• Making sure all participants have the same experience
• Every aspect of their experience is _________• Room is checked and reset
between each participant
• Confederate(s) behavior is all scripted
Experiments = Control• Example:
• Experiment designed to test effectiveness of new test-taking strategy• Experimental group: Comes to lab and is trained and
tested in groups• ______ group: Takes test at home online
Experiments = Control• Example:
• Experiment showed those trained in the new strategy got higher scores
• What might have caused this effect?• Home distractions, “_________,” social facilitation, etc.
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Experiments = Control• Example:
• Experiment designed to test effectiveness of learned test-taking strategy• Experimental group: Comes to lab, is trained in
groups, then tested
• Control group: Comes to lab, is trained in an unrelated task in groups, then tested
• Experiment showed those trained in the new strategy got higher scores• Since everything was the same except for IV, the
IV likely ________ the effect
Experiments = Control• Experiments cannot control everything
• What if control and experimental groups just happened to differ in intelligence?• We cannot make everyone coming into the lab
have equal intelligence, schooling, etc.
• Randomization = _________• Whatever cannot be controlled can be randomized between conditions• With just 30 people in each condition, most
participant factors get spread out evenly
Experiments Uncover Causation• Through control of environmental factors and randomization of participant factors…• We can know exactly what affects the DV in the experimental groups
• Rules out possible “confounds”• Any variable (environmental/ participant) that
varies along with the ____ and affects the ____
• E.g., Distractions at home (confound) only being present in control group (varies along with IV) affecting test scores (affects the DV)
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Experiments Uncover Causation• Good experiments = High “______ validity”
• Ability to know exactly what is affecting the DV
• That’s the hallmark of good science!
• All sciences, at their core, are methods of understanding cause and effect
The Basic Experiment• “_____________ Design”
• Participants randomly assigned to…• Experimental Group –
Includes the affecting IV• Control Group – Doesn’t
include the affecting IV
• After the manipulation, the DV is measured in the same way for both groups
Virus Saline
The Basic Experiment• Example: Bargh, Chen, & Burrows, 1996
• Hypothesis: Subtle primes can affect behavior• Experimental Group – Completed word unscrambling
task, where many of the words were related to the ______ (e.g., wrinkle, grey, wise)
• Control Group – Completed similar word unscramb-ling task that didn’t include any elderly-related primes
• After manipulation, experimenters recorded the time it took participants to exit the lab room
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The Basic Experiment• Example: Bargh, Chen, & Burrows, 1996
• It was expected that those primed with elderly-related words would walk _______ when exiting the study (emulating the elderly)• That’s exactly what
they found across two studies
The Basic Experiment• Example: Daniel Pink’s DRIVE (2010)
• Hypothesis: Higher pay hinders quality of work, because it leads to job-related _______• Computer programmers in India asked to create new
database program (like Excel)• Experimental Group – participants given 2 months
salary for 2 days work• Control Group – given 2 days salary for 2 days work
• Afterward, their work (the program) was judged according to its efficacy and elegance (DVs)
The Basic Experiment• Example: Daniel Pink’s DRIVE (2010)
• Found those who received 2 days salary created a much better product than those paid 2 months salary
• In both examples…• Everything was kept constant between groups
except for the IV• E.g., primed words, salary
• So, even if the results are a bit hard to believe, they were most likely caused by the IV
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• Advantages• Can be used to infer _________
• Produces results that are clear and easy to understand
• Disadvantages• Cannot test most participant variables as IVs
• E.g., income, intelligence, personality
• Since you cannot directly __________ these factors, you cannot infer that they affect the DV
Basic Experiments
More Complex Experiments• To provide more evidence of an effect, experi-menters can test ______________ of the IV
• Example: Bargh, Chen, & Burrows, 1996• Hypothesis: Subtle primes can affect behavior
• Experimental Group #1 – primed with words related to rudeness (e.g., bother, disturb, annoy)
• Experimental Group #2 – primed with words related to politeness (e.g., considerate, patient, courteous)
• Control Group – primed with words unrelated to either rudeness or politeness
More Complex Experiments• Example: Bargh, Chen, & Burrows, 1996
• Participants told to contact experimenter standing outside• Experimenter talked with
someone else, ignoring participant for up to 10 minutes, unless interrupted
• Recorded whether partici-pant “rudely” interrupted experimenter
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More Complex Experiments• Example: Daniel Pink’s DRIVE (2010)
• Repeated previous experiment, but added a third group that got paid 2 weeks salary
Perfo
rman
ce
Low
Med
High
2-days pay 2-months pay2-weeks pay
More Complex Experiments• By adding extra levels to the IV…
• Able to ________ effects of IV multiple times• Adds to internal validity (believability) of the results
• E.g., showing effect of priming through both rudeness- and politeness-related words
• Able to show exactly how the IV affects the DV• E.g., at what point does an increased salary begin
to impede performance
Perfo
rman
ce
Low
Med
High
2-days pay 2-months pay2-weeks pay
• Participants assessed both before and after the manipulation• Often used to assess the effectiveness of
“___________”• Example: Effect of behavioral therapy on smoking
• Number of cigarettes smoked per day is recorded• Experimental group: Participants put on fixed
schedule for smoking less and less• Control group: Participants are allowed to lessen
smoking in any way they wish• After 1 month, # of cigarettes per day is assessed
Pretest Posttest Designs
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• Example: Effects of behavioral therapy on smoking
Pretest Posttest Designs
# of
Cig
aret
tes
per D
ay
1
> 10
Pretest Posttest
5
Experimental group
Control group
• _______ – participants who drop out mid-study
• Creates problems if participants who drop out are different from those who stay in
Pretest Posttest Designs
# of
Cig
aret
tes
per D
ay
1
> 10
Pretest Posttest
5
Experimental group
Control group
• Example: Effects of behavioral therapy on smoking• Does this necessarily mean the treatment worked?
• What if half the experimental group dropped out of the study before it was completed?
• Difference between mortality and non-mortality pars.
• Many people who were heavy smokers dropped, because they couldn’t handle the treatment
Effect of Mortality
# of
Cig
aret
tes
per D
ay
1
> 10
5
Participants who dropped
Participants who stayed
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• Example: Effects of behavioral therapy on smoking
Effect of Mortality
# of
Cig
aret
tes
per D
ay
1
> 10
Pretest Posttest
5
Experimental group
Control group
Treatment had no effect, except driving away heavy smokers
• Example: Wierzbicki & Pekarik, 1993• Meta-analysis of 125 studies testing effectiveness
of psychotherapy
• Discovered an average of 47% of participants dropped out of each study before its completion
• Which participants were most likely to drop?• Those with more _______ psychological illness
• Dropped because of hospitalization, jailing, suicide, distrust of therapist (paranoia), etc…
• Those who weren’t _______ from therapy
Effect of Mortality
• Advantages• Can be a good way to clearly display effects of
treatment vs. non-treatment
• Sometimes it’s ________ to have a control group (e.g., depriving people of beneficial treatment)
• Helps effect of IV to stand out with fewer pars.Effect of treatment is often clouded by between-person variability• By assessing the same participants before and after
treatment, you take away this extra “noise” in the data
Pretest Posttest Designs
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• Example: Testing effect of social rejection on self-esteem• Posttest only design: effect of IV has to rise above
within-group variability in DV
Pretest Posttest Designs
Self-
este
em
Low
High
Social Rejection Group (Experimental)
Medium
No Social Rejection Group (Control)
• Example: Testing effect of social rejection on self-esteem• Pretest posttest design: effect of IV is shown in each
individual
Pretest Posttest Designs
Self-
este
em
Low
High
Before Social Rejection
After Social Rejection
Medium
• Effect _________ much more• Each individual participant acts as a replication of
the effect
Pretest Posttest Designs
Self-
este
em
Low
High
Before Social Rejection
After Social Rejection
Medium
(Average Effect of Rejection)
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• Disadvantages• __________
• Have to make sure most participants stick with the experiment right to the end
• Should track participants who drop out
• Figure out if they are significantly different from those who stay in
Pretest Posttest Designs
• Try to make experiment as short as possible (days vs. weeks makes a big difference)
• Offer _________ (e.g., cash) for returning
• Make it clear how important it is for participants to keep coming back
Pretest Posttest Designs• How can you lessen mortality rates?
• Disadvantages• ______ Effects – simply taking a pretest can affect
the posttest measure
• Practice effect – repeated performance of the same test leads to better performance over time• E.g., taking the same IQ test over and over again
• __________ effect – pretest sensitizes or desensitizes participants to the manipulation (changes reaction)• How might exposure self-esteem measure affect
reactions to subsequent social rejection?
Pretest Posttest Designs
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• Disadvantages• ______ Effects – simply taking a pretest can affect
the posttest measure
• _______ effect – pretest clues participants into what the hypothesis is
Pretest Posttest Designs
• Most participants want to help the experimenter
• May fake what they think is the desired reaction
• Increase the ____ between pre- and posttest• Participants tend to forget about the pretest pretty quickly
• Add ________ tasks between pre- and posttest• E.g., have participants play a video game
• Try to use pre-tests that seem unrelated to the manipulation• E.g., use an implicit measure of self-esteem (testing
association between self and positive vs. negative words)
Pretest Posttest Designs• How can you lessen order effects?
Type of Participant Usage• ______________ Design – participants are randomly assigned to experimental or control conditions
• ________________ Design – participants are run through both experimental and control conditions• E.g.,
• Participants play round of cyberball where they are rejected• Self-esteem is measured• Participants play round of cyberball where they aren’t
rejected• Self-esteem is measured again
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Repeated Measures Design• Advantages
• Requires far _______ participants• Saves lots of time /
resources
• Some samples are very difficult/ expensive to attain• E.g., studying effects
of stress on expert meditators (monks from Tibet)
Repeated Measures Design• Advantages
• Cuts out “______” in data caused by individual variability• Helps effects to better stand out
• Sometimes exposure to one condition after another is more naturalistic• E.g.,
• Testing effects of TV ads on mood
• Examining effects of political slogans on attitudes• Investigating effects of online dating profiles on mate
preferences
Repeated Measures Design• Disadvantages
• Again, there is the problem of ______ effects• Example:
• In first round of cyberball, participants are rejected and then their self-esteem is measured
• In second round of cyberball, participants are not rejected and then their self-esteem is measured
• How might participants interpret this order of events?
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Repeated Measures Design• Disadvantages
• If study contains many conditions, the experiment can end up being really long
• Danger of “_______” participants
• Could cause “satisfyzing”• Participants stop
caring enough to perform to the best of their ability
Better Repeated Measures Design• Counterbalancing can nullify order effects
• Participants assigned to different order of conditions• Allows order effects to cancel
each other out• E.g., initial rejection lowers
self-esteem, but initial acceptance heightens self-esteem
• Allows experimenter to examine differences caused by ______ effects
Making the Most of Participants• ____________ Design - participants are prescreened
and then assigned to different conditions • Important participant factors are equalized between
conditions• E.g., Study of effects of social rejection on self-esteem
• Use prescreening measure of self-esteem• Assign equal numbers of low and high esteem
participants to each condition• Removes “noise” caused by participant factors
• But, you don’t have to worry about order effects, fatigue, or other pitfalls of repeated measure designs
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• Example: Effect of social rejection on self-esteem• Without prescreening, experimental and control
groups may just happen to differ in self-esteem• Especially likely if sample size is ______
Matched Pairs Design
Self-
este
em
Low
High
Group 1 Group 2
Medium
• Example: Effect of social rejection on self-esteem• With prescreening, you can randomly assign same
number of low- and high-self esteem participants to each condition
Matched Pairs Design
Self-
este
em
Low
High
Group 1 Group 2
Medium
Overview• Experiments show _________ through control or randomization of everything that affects participants
• Different types of experimental designs:
• Posttest only design
• Pretest posttest design
• Independent groups design
• Repeated measures design
• Matched pairs design