文档介绍：Experiment Basics: Variables
Psych 231: Research Methods in Psychology
Lab reminders
Print out the Class experiment exercise (from the Lab web page) and bring it to labs this week
Group project introduction sections due this week
Many kinds of Variables
Independent variables (explanatory)
Dependent variables (response)
Extraneous variables
Control variables
Random variables
Confound variables
Identifying potential problems
These are things that you want to try to avoid by careful selection of the levels of your IV (may be issues for your DV as well).
Floor and ceiling effects
Demand characteristics
Experimenter bias
Reactivity
Range effects
Floor: A value below which a response cannot be made
As a result the effects of your IV (if there are indeed any) can’t be seen.
Imagine a task that is so difficult, that none of your participants can do it.
Ceiling: When the dependent variable reaches a level that cannot be exceeded
So while there may be an effect of the IV, that effect can’t be seen because everybody has “maxed out”
Imagine a task that is so easy, that everybody scores a 100%
To avoid floor and ceiling effects you want to pick levels of your IV that result in middle level performance in your DV
Demand characteristics
Characteristics of the study that may give away the purpose of the experiment
May influence how the participants behave in the study
Examples:
Experiment title: The effects of horror movies on mood
Obvious manipulation: Having participants see lists of words and pictures and then later testing to see if pictures or words are remembered better
Biased or leading questions:
Don’t you think it’s bad to murder
unborn children?
Experimenter Bias
Experimenter bias (expectancy effects)
The experimenter may influence the results (intentionally and unintentionally)
., Clever Hans
One solution is to keep the experimenter (as well as the participants) “blind” as to what conditions are being tested
Knowing that you are being measured
Jus