1. Research Variables

2. Research Definitions
An experiment is a process in which an investigator devises two or more different experiences (treatments) for subjects or participants.
Involves a control group and one or more treatment groups

3. Research Variables
Independent Variable (IV): the controlled variable in a study; hypothesized to have an effect on the dependent variable
In a true experiment, this is an experimental (manipulated) variable.
In a quasi-experiment, this is a subject variable (not subject to manipulation).
Experimental
Types of Independent Variables:
Experimental: systematically controlled or manipulated by the experimenter; levels are set and participants are assigned to the different levels
Subjects (Organismic): a characteristic of the participant; not subject to manipulation e.g. intelligence, personality, etc.
The type of variable affects the type of analyses performed and the way the results of statistical analyses are interpreted
To determine, ask: did the condition exist for the subject prior to the experiment?
Some variables could go either way (usually environmental variables) e.g. lighting, noise, temperature
Levels of the Independent Variable:
An independent variable can have two or more levels
Levels can be independent or dependent (before and after; matched subjects)
Subject

4. Research Variables
Regardless of type, there will always be two or more levels of the independent variable.
Variable: a characteristic or phenomenon that may take on different values; variables must vary!
The levels of the independent variable can be:
Independent of one another: between-subjects design
Dependent on one another: within-subjects design

5. Research Variables
Dependent Variable (DV): an outcome of interest that is observed and measured by the researcher; hypothesized to be affected by the independent variable

6. Defining Research Variables
Operational Definition: a definition of a variable in terms of the operations used to manipulate it or measure it
Must be precise enough that anyone reading a review of your research could replicate your experiment exactly.

7. Problem Variables
Extraneous (Nuisance) Variables: uncontrolled variables which can affect the experimental outcome
Extraneous variables become confounding variables when their values change systematically along with the independent variable in an experiment.