2. Variables vs. constants
• Measured variables
– Dependent
– Observed
• Manipulated variables
– Independent
– Controlled
• Four categories of variables
3. Research Variables
• There are four general categories of
variables.
– Situation variables
– Response variables
– Individual differences in participants variables
– Mediating variables
4. Mediating Variables
• Inferred psychological processes that are
often used to explain research outcomes.
– These variables are invented by the experimenter
and are related to the theory that produced the
experiment.
• Operational Definitions
– Measured variables must be defined clearly
4
8. • Experimental methods systematically
manipulate and measure variables.
• Causality must consider:
– Temporal order (precedence)
– Covariation between variables (cause and effect)
– Other explanations for the change must be
eliminated
Experimental Methods
9. Experimental vs Field Studies
• External validity
– Non-experimental field studies are more realistic
but extraneous variables are less controlled
• Ethical and practical concerns limit what
can be manipulated and controlled
10. Research Validity
• Valid: reasonable, accurate, and
justifiable
–External validity
• Generalizability
–Internal validity
• The extent of the relationship between two variables
–Construct validity
• How well the variables are measured or manipulated
