PS295 Lecture Notes - Lecture 13: Random Assignment, Blind Experiment, Internal Validity
Additional Threats to Internal Validity:
-in addition to the seven classic threats of Campbell and Stanley 1966 (need to know) other factors can
affect internal validity of a study
1) Experimenter expectancies
-aka observer expectancy effect
-researcher's expectations regarding how participants will (or should) respond to an IV and can distort
the results of an experience
-expectancies can affect how researcher interprets participants' behaviour
-if you expect something to happen, you're more likely to see it happen (Rosenthal effect)
-double blind experiment: no one knows who has received what IV
2) Demand characteristics
-participant expectancy effect
-participants' assumptions about the nature of a study can affect their behaviour
-reactivity occurs when participants respond to cues from the experimental setting rather than the IV
-can be cooperative or uncooperative in nature
-researchers may unintentionally communicate their expectations to participants
3) Placebo effects
-participant expectancy effect
-physiological or psychological changes that occur as the result of a mere suggestion that these changes
will occur
Document Summary
In addition to the seven classic threats of campbell and stanley 1966 (need to know) other factors can affect internal validity of a study. Researcher"s expectations regarding how participants will (or should) respond to an iv and can distort the results of an experience. Expectancies can affect how researcher interprets participants" behaviour. If you expect something to happen, you"re more likely to see it happen (rosenthal effect) Double blind experiment: no one knows who has received what iv: demand characteristics. Participants" assumptions about the nature of a study can affect their behaviour. Reactivity occurs when participants respond to cues from the experimental setting rather than the iv. Researchers may unintentionally communicate their expectations to participants. Physiological or psychological changes that occur as the result of a mere suggestion that these changes will occur. Occur when a treatment is confounded with participants" knowledge that they are receiving a treatment.
