2. Road Map
• Turn in Reflection Assignment #1
• Announcement about lab
• Quick Review
• Finish Chapter 6
3. About Lab
• Go to class
• Turn in assignments
• Starting group project this week—you can’t
contribute fully if you aren’t there!
• Remember: can be dropped after 4 absences
• If you fail lab, you fail the course
• Pay close attention to detail
6. Threats to Construct Validity
• Factors that impact how well our
operationalizations actually represent
constructs
• Pg 171, Table 6.2 – long list of threats
• We will focus on two major ones:
– Participant reactivity to the experimental situation
– Experimenter effects
7. Participant Reactivity to the
Experimental Situation
• Participants’ motives and perceptions
• Demand characteristics
• Positive self-presentation
8. Instruction set #1
We want to see how well you are able to learn
the following sets of letters. Letters will appear
in groups of 3 to 7, and each letter will appear
on the screen for 1 second. Following the
presentation of the letters, …
9. Instruction Set #2
In the following task, you will be presented with
groups of letters ranging from 3 to 7 letters.
Each letter will appear on the screen for one
second. Your task is to…
10. Experimenter effects
• Researcher actions and characteristics that
influence the responses made by the research
participant
• Expectancies
– Clever Hans
• Attributes
– Biosocial
– Psychosocial
– Situational factors
12. Internal Validity
• The extent to which we can accurately
infer that the independent and
dependent variables are causally related
Independent Observed Effect
Variable (DV)
13. Causally Related
Independent Observed Effect
Variable (DV)
Cause and effect are Cause must No other explanation
related (covary) precede effect is plausible
15. Threats to Internal Validity
• History
• Maturation
• Instrumentation
• Testing
• Regression Artifact
• Attrition
• Selection
• Additive and Interactive Effects
16. History
• Any event occurring after the study begins that
could produce the observed outcome
• Differential history: only one group experiences
history event
• Note what history is NOT
17. Maturation
• Changes in biological and psychological conditions
that occur with the passage of time
– Factors within the individual
• Example: Head Start program and achievement
over a school year
18. Instrumentation
• Changes in the assessment/measurement of the
dependent variable
• Example: multiple observers and interviewers
19. Testing
• Changes in a person’s score on the second
administration of a test are a result of
previously having taken the test
• Example: pre-test and post-test on memory
task
20. Regression Artifact
• a.k.a. regression toward the mean
• The tendency for extreme scores to become less
extreme on a second assessment
21. Attrition
• Participant drop-out
– Don’t show up for appointment
– Decide to discontinue study
• Differential attrition is especially problematic
22. Selection
• The choice of participants for the various
treatment groups based on different criteria
– NOT random assignment
23. Additive & Interactive Effects
• The combined effect of several threats to
internal validity
24. External Validity
• The extent to which the results of the
experiment can be generalized across
variations in:
– people
– Settings
– Treatments
– Outcomes
– Time
25. What Limits External Validity?
• Lack of random selection/sampling
• Chance factors
• IV-DV relationship varies across levels of
another variable
26. 5 main categories of external validity
• Population Validity
• Ecological Validity
• Treatment Variation Validity
• Outcome Validity
• Time Validity
27. Population Validity
• The extent to which the results of a study can
be generalized to the larger population.
• Target population: the population to which
we want to generalize the results
• Accessible population: the population of
research participants available to the
investigator
28. Ecological Validity
• The extent to which the results of a study can be
generalized across settings or environmental conditions
• Which research setting receives the most criticism here?
– laboratory
29. Temporal Validity
• The extent to which the results of an experiment can be
generalized across time
