Research methods
Experiments
Definition of an Experiment
An experiment is an investigation that looks for a cause-and-effect relationship
between variables. The researcher manipulates one variable and measures its
effect on another
(Research Methods section: Experiments)
Variables in Experiments In research, manipulate means to
deliberately change or control
something to see what effect it has
Independent Variable (IV) on something else.
The independent variable is the variable that the researcher manipulates to create different
conditions or levels
(Research Methods section: Experiments – Key Terms) 
Dependent Variable (DV)
The dependent variable is the variable that is measured and is expected to change as a result
of the IV
(Research Methods section: Experiments – Key Terms)
Example from the book:
• IV: Light level (high vs low)
• DV: Attention or concentration
(Research Methods section: Experiments)
Extraneous and Confounding Variables
An extraneous variable is any variable other than the IV that could influence the DV
(Research Methods section: Experiments) 
A confounding variable is an extraneous variable that systematically affects one condition
of the IV, making it impossible to determine whether the IV caused the change in the DV
(Research Methods section: Experiments) 
! If confounding variables are not controlled, the validity of the experiment is reduced
(Research Methods section: Experiments)
, Types of Experiments
Laboratory Experiments
A laboratory experiment is conducted in a controlled environment that is not the
participant’s natural setting
(Research Methods section: Laboratory experiments) 
Strengths
• High control of variables
• High reliability
• Easier replication
(Research Methods section: Laboratory experiments) 
Weaknesses
• Lower ecological validity
• Increased risk of demand characteristics
(Research Methods section: Laboratory experiments)
Field Experiments
A field experiment is conducted in a natural environment, but the IV is
still manipulated by the researcher
(Research Methods section: Field experiments)
Natural Experiments
A natural experiment occurs when the IV cannot be manipulated
and naturally exists
(Research Methods section: Natural experiments)
Experiments
Definition of an Experiment
An experiment is an investigation that looks for a cause-and-effect relationship
between variables. The researcher manipulates one variable and measures its
effect on another
(Research Methods section: Experiments)
Variables in Experiments In research, manipulate means to
deliberately change or control
something to see what effect it has
Independent Variable (IV) on something else.
The independent variable is the variable that the researcher manipulates to create different
conditions or levels
(Research Methods section: Experiments – Key Terms) 
Dependent Variable (DV)
The dependent variable is the variable that is measured and is expected to change as a result
of the IV
(Research Methods section: Experiments – Key Terms)
Example from the book:
• IV: Light level (high vs low)
• DV: Attention or concentration
(Research Methods section: Experiments)
Extraneous and Confounding Variables
An extraneous variable is any variable other than the IV that could influence the DV
(Research Methods section: Experiments) 
A confounding variable is an extraneous variable that systematically affects one condition
of the IV, making it impossible to determine whether the IV caused the change in the DV
(Research Methods section: Experiments) 
! If confounding variables are not controlled, the validity of the experiment is reduced
(Research Methods section: Experiments)
, Types of Experiments
Laboratory Experiments
A laboratory experiment is conducted in a controlled environment that is not the
participant’s natural setting
(Research Methods section: Laboratory experiments) 
Strengths
• High control of variables
• High reliability
• Easier replication
(Research Methods section: Laboratory experiments) 
Weaknesses
• Lower ecological validity
• Increased risk of demand characteristics
(Research Methods section: Laboratory experiments)
Field Experiments
A field experiment is conducted in a natural environment, but the IV is
still manipulated by the researcher
(Research Methods section: Field experiments)
Natural Experiments
A natural experiment occurs when the IV cannot be manipulated
and naturally exists
(Research Methods section: Natural experiments)
