Chapter 5: Introduction to
Experimental Research
Research uses 2 methods:
● method of agreement → if X then Y → accomplished via experimental group
● method of disagreement → if not X then not Y → accomplished via control group
both criteria are never fully met in research → joint method should be the standard
Experiment: systematic research in which the investigator directly varies some
factor(s), holds all others constant, and observes the results of the variation
- Independent variables: controlled by experimenter (subject of interest)
- Subject variables: preexisting participant characteristics (e.g. gender)
- Extraneous variables: held constant
- Dependent variables: measured behaviours
1. Manipulated Independent Variables
Minimum of 2 levels (a.k.a., conditions). Types of independent variables:
- Situational variables: can be encountered in natural environments
- Task variables: tasks to be executed by participants
- Instructional variables: same task executed in different ways by diff participants
- Control/experimental group: placed in treatment or comparison group
2. Subject Variables
With manipulated variables, conclusions about the causes of behaviour can be made
with some degree of confidence; with subject variables, causal conclusions cannot be
drawn. The reason has to do with the experimenter’s amount of control. With
manipulated variables, the experiment can meet the criteria for demonstrating causality.
3. Extraneous Variables
Confounder: uncontrolled extraneous variable that covaries with the independent
variable and could provide an alternative explanation for the results.
4. Dependent Variables
Ceiling effect: when the average group scores are so high that no difference can be
determined between conditions
Experimental Research
Research uses 2 methods:
● method of agreement → if X then Y → accomplished via experimental group
● method of disagreement → if not X then not Y → accomplished via control group
both criteria are never fully met in research → joint method should be the standard
Experiment: systematic research in which the investigator directly varies some
factor(s), holds all others constant, and observes the results of the variation
- Independent variables: controlled by experimenter (subject of interest)
- Subject variables: preexisting participant characteristics (e.g. gender)
- Extraneous variables: held constant
- Dependent variables: measured behaviours
1. Manipulated Independent Variables
Minimum of 2 levels (a.k.a., conditions). Types of independent variables:
- Situational variables: can be encountered in natural environments
- Task variables: tasks to be executed by participants
- Instructional variables: same task executed in different ways by diff participants
- Control/experimental group: placed in treatment or comparison group
2. Subject Variables
With manipulated variables, conclusions about the causes of behaviour can be made
with some degree of confidence; with subject variables, causal conclusions cannot be
drawn. The reason has to do with the experimenter’s amount of control. With
manipulated variables, the experiment can meet the criteria for demonstrating causality.
3. Extraneous Variables
Confounder: uncontrolled extraneous variable that covaries with the independent
variable and could provide an alternative explanation for the results.
4. Dependent Variables
Ceiling effect: when the average group scores are so high that no difference can be
determined between conditions
