Validity Threats Flashcards
(44 cards)
What are the different kinds of validity
– Internal
– External
– Statistical
An experiment is the most important tool to…
identify cause-effect relationships:
What is a cause and effect relationship
In an experiment we control the cause and
observe the effect.
Changes in the DV are caused by the
manipulation of the IV.
What is internal validity
The extent to which the results obtained are a function of the variables that were systematically manipulated.
Examples of internal validity
- Are changes in the IV responsible for the observed variation in the DV?
- Might the variation in the DV be attributable to other causes? (confounds)
Why is internal validity important
We often conduct research in order to determine cause-and-effect relationships.
Can we conclude that changes in the independent variable caused the observed changes in the dependent variable?
High internal validity =
Strong evidence of causality.
Low internal validity
Little or no evidence of causality.
To maximise internal validity:
●Must be able to rule out the possibility of other factors producing the change (confounds).
●Must control everything and eliminate possible extraneous influences.
●Easiest in highly controlled, laboratory settings.
Threats to internal validity compromise our confidence in saying that
a relationship exists between the IV and DV.
Threats to internal validity compromise our confidence in saying that a relationship exists between the IV and DV. They include:
●History effects ●Maturation effects ●Mortality ●Instrument decay ●Participant selection ●Statistical regression to the mean
History effects:
Events occurring during the experiment that are not part of the treatment.
History effect example and solution
During the experiment, a fire alarm goes off which affects one group.
Solution: Hold experiences constant except for IV; randomly assign conditions to time.
Maturation effects
Biological or psychological processes within participants that may change simply due to the passing of time.
Maturation examples
– Aging
– Fatigue
– Hunger
These changes occur naturally over time, and influence the results of a research study.
Mortality effects
The differential loss of individuals from treatment and/or control groups due to nonrandom reasons.
Mortality problem and solution
Problem: Those who drop out of your study could be qualitatively different from those who remain.
Solution: Try to stop people dropping out, e.g., provide an inconvenience allowance.
Instrument Decay:
Measuring devices change over time.
Equipment becomes inaccurate with age.
Experimenters become more skilled, or bored.
Instrument decay solution
Randomise condition to time, check reliability of instruments, train staff.
Participant Selection:
Different types of participants placed at the different levels of the IV.
Participant selection and solution
–Example: Only males in control group and only females in experimental group.
–Example: If you test different groups at different times, then people will be different.
Solution: Random assignment, matching.
When participants communicate…
this effects…
●Effects equalising groups
–Diffusion of treatment effects
–Compensatory rivalry
–Compensatory equalisation
●Effect separating groups
–Resentful demoralisation
Diffusion of Treatment:
Occurs if the control group learns about the manipulation.
Can occur when participants talk about an ongoing experiment.
Do not debrief any participants until ALL participants have finished.
Compensatory Rivalry:
When participants in different conditions start competing.
Example:
If participants become aware that they are in the control group, they may work harder to overcome the ‘disadvantage’ of being in the control group.
Saretsky (1972) named this the “John Henry effect”
