2. Example
• Hypothesis: Eating candy with peanuts
improve memory performance
• How might we test this with an
experiment?
3. Constants vs. Variables
• Characteristics of the psychological
situations
– Constants: have the same value for all individuals in
the situation
– Variables: have potentially different values for each
individual in the situation
Constants:
• M&Ms are eaten
Variables:
• Type of M&M: peanut vs plain
• Memory performance
4. Variables
• Conceptual vs. Operational
– Conceptual variables (constructs) are abstract
theoretical entities
– Operational variables are defined in terms within
the experiment. They are concrete so that they
can be measured or manipulated
Conceptual
Peanut candies
Memory
Operational
Peanut M&Ms
Memory test
Underlying
assumptions
5. Manipulating the IV
• Straightforward manipulations
– Stimulus manipulation - different conditions use
different stimuli
– Instructional manipulation – different groups are
given different instructions
• Staged manipulations
– Event manipulation – manipulate characteristics of
the context, setting, etc
8. Strength of Manipulation
• The strength of a manipulation can effect how
results are interpreted
– Maximizes difference between groups
– Increases likelihood IV will effect the DV
9. Cost of Manipulation
• Funding limitations
– Staged is usually more costly than straightforward
10. Choosing your dependent
variable
• How to measure your construct:
–Can the participant provide self-report?
–Is the dependent variable directly
observable?
• Choice/decision
–Is the dependent variable indirectly
observable?
• Physiological measures
• Behavioral measures
11. Self-Report Measures
• Used to measure aspects of human
thought and behavior:
–Attitudes
–Judgments about oneself or another
–Emotional states
–Confidence
Rating Scale:
Strongly Disagree --------- Strongly Agree
15. Sensitivity
• The dependent variable should be
sensitive enough to detect differences.
• Floor Effect
– A value below which a response cannot be made
• Ceiling Effect
– When the dependent variable reaches a level that
cannot be exceeded
16. Choosing your dependent
variable
• Conceptual level: Memory
Operational level: Form of
memory test
e.g.: Memorize a list of words
while eating the candy
Then 1 hour after study time,
recall the list of words
Measure the accuracy of recall
17. Extraneous Variables
• Control variables
–Holding things constant
• Controls for excessive random variability
•Number of M&Ms consumed
•Time of day test taken
18. Extraneous Variables
• Random variables
–Desire equal variability across all
experimental conditions
–Randomization
What your participants ate
before the experiment.
19. Control Considerations
• Participant Expectations
–Demand Characteristics
• Cues may allow participants to figure out
experiment
• Influences how they behave
23. Additional Considerations
• Write thorough Research Proposal
• Pilot Study
– Trial run
• Manipulation Checks
– Measures if the IV effects DV
• Debriefing
– meeting with the participants after the conclusion
of the study to discuss
