Internal and External Validity Flashcards
Random Error
Chance difference between the observed and true values of something i.e. participants not understanding the task instructions
Systematic Error
A consistent difference between the observed and true values of something i.e. a typo in the instructions
Selection Biases
-Differences exist between the two groups prior to the manipulation of the IV
- Control through random assignment
History Effect
- Occurs when an event outside the study effects the outcome of the study
- Control through conducting the experiment over a short period of time and randomisation
Maturation Effect
-Occurs when changes within participants of a study changes the outcome of study
- Control through randomisation and conducting the experiment over a short period of time
Learning/ Practice Effect
- Result in better post-test performance because participants in a group have become more familiar with some aspect of the experiment from the pre-test
- Control through a post-test only design
Experimental Fatigue
- Experimental situations can lead to physical/mental fatigue
- Control through matching the amount of required effort across all experimental conditions
Order Effects
-Occurs when the effect on the IV is different depending on which experimental condition/ DV measurement is experienced first
- Control through randomising the order in which participants experience the experimental conditions
Carry-over Effects
-Occurs when the effects of a prior experimental condition continues to influence a participants performance in a later condition
- Control through the inclusion of a washout period between experimental conditions
Attrition Effect
-Participants will often drop out of a study
- This is a problem for internal validity if attrition is different across all conditions and systematically related to the IV
- Control by providing incentives to stay in the study
Expectancy Effects
- Occurs when the experimenter subtly communicates their expectations to the participants, who alter their behaviour to conform to these expectations
-Control by training experimenters well
. Blinding experiments
. Using multiple experimenters
Motivated Reasoning in a study design
- Occurs when the experimenters own personal biases influence the design of the study to make a specific outcome more likely
- Control through peer review of study protocols
Reactivity
-Occurs when individuals alter their performance or behaviour due to the awareness that they are being observed.
- Control through .Deception
. Blinding
.Engaging tasks or habituation
Demand Characteristics
- Any cue i.e. rumors about the study, communication between participants etc. that is outside the actual experimental situation
that may guide or bias a participants behaviour - These cues may lead to the participants guessing the hypothesis and taking on a certain role in response.
