RESEARCH METHODS
3. Experimental Research
EXPERIMENTAL RESEARCH
• Experiment: Manipulation of one variable under
controlled conditions so that resulting changes in
another variable can be observed.
• Detection of cause-and-effect relationships
• How does X affect Y?
• X = Independent Variable
• Y = Dependent Variable
• Independent variable (IV): variable that is manipulated
• Dependent variable (DV): variable that is measured
EXPERIMENTAL RESEARCH
• Population: entire group
• Sample: subset of the population
• Random Sampling or Random Selection:
Each member of a population has an
equal chance of being selected.
• Unbiased; objective
• Sampling bias: Occurs when a sample is
NOT representative of the population.
• If the sample is biased, the results are
NOT valid
EXPERIMENTAL RESEARCH
• Experimental Group: receives special treatment (IV)
• Control Group: does not receive special treatment (IV)
• Manipulate IV for one group only
• Resulting differences in the two groups must be
due to the IV
• Random Assignment: assignment of participants to
groups by chance
• Reduces extraneous variables
• Reduces bias
EXPERIMENTAL RESEARCH
• Extraneous Variable: Any variables other than the
independent variable that may influence the
dependent variable in a study.
1. Situational
2. Participant
3. Experimental
• Confounding of Variables: When the effects of an
extraneous variable are difficult to separate from
the effects of the independent variable.
• Influences the dependent variable
EXPERIMENTAL RESEARCH
• Experimenter Bias: experimenter’s expectation
influence outcome
• Participant Bias: participant's expectation
influence outcome
• Placebo Effect: Occurs when a participant’s
expectations produce change even though they
receive a “fake” treatment.
• Hawthorne Effect: The tendency of individuals
to perform better simply because of being
singled out and made to feel important.
EXPERIMENTAL RESEARCH
• Double-blind: BOTH the participants and the
experimenters remain unaware of which
participants are in the experimental group and
control group.
• This eliminates both participant bias
and experimenter bias
• Used for drug trials
EXPERIMENTAL RESEARCH
EXPERIMENTAL VARIATIONS
• Expose a single group to two different conditions
-Reduces extraneous variables
• Manipulate more than one independent variable
- Allows study of interactions between variables
• Measure more than one dependent variable
- Obtains a more complete picture of effect of
the independent variable
EXPERIMENTAL RESEARCH
Description: Manipulation of one
variable under controlled conditions so
that the resulting changes in another
variable can be observed.
Advantages
• Shows cause and effect
relationship!!!
• Manipulation of variables
• Precise Control
• Generalizability
Disadvantages
• Artificial situations
• Costly
• Ethical issues