1. Experimental Research
Designs
Dr Nida Zafar
Assistant Professor
PhD Applied Psychology
Email. nida.zafar@lgu.edu.pk
Institute of Applied Psychology
University of the Punjab, Lahore
2. Why Psychologist Conduct Experiments
1. Researchers conduct experiments to test hypotheses
about the causes of behavior.
2. One of the primary reasons that psychologists
conduct experiments is to make empirical tests of
hypotheses they derive from psychological theories.
3. Why Psychologist Conduct Experiments
3. Experiments allow researchers to decide whether a treatment
or program effectively changes behavior
Well-conducted experiments also help to solve society’s problems by
pro- viding vital information about the effectiveness of treatments in a
wide variety of areas. This role of experiments has a long history in the
field of medicine
4. LOGIC OF EXPERIMENTAL RESEARCH
• Researchers manipulate an independent variable in an experiment to observe
the effect on behavior, as assessed by the dependent variable.
• Experimental control allows researchers to make the causal inference that the
independent variable caused the observed changes in the dependent variable.
• •
5. LOGIC OF EXPERIMENTAL RESEARCH
Control is the essential ingredient of experiments; experimental control is
gained through
1. Manipulation
2. Holding conditions constant
3. Balancing
6. LOGIC OF EXPERIMENTAL RESEARCH
An experiment has internal validity when it fulfills the three conditions required for
causal inference
1. Covariation (Covariation is met when we observe a relationship between the
independent and dependent variables of an experiment)
2. Time-order relationship (A time-order relationship is established when
researchers manipulate an independent variable and then observe a subsequent
difference in behavior (i.e., the difference in behavior is contingent on the
manipulation).
3. Elimination of plausible alternative causes (A time-order relationship is
established when researchers manipulate an independent variable and then
observe a subsequent difference in behavior (i.e., the difference in behavior is
contingent on the manipulation).
7. LOGIC OF EXPERIMENTAL
RESEARCH
• When confounding occurs, a plausible alternative
explanation for the observed covariation exists, and
therefore, the experiment lacks internal validity.
• Plausible alternative explanations are ruled out by
holding conditions constant and balancing.
8. Characteristics of True Experiment
• A true experiment involves the manipulation of one or more factors and the
measurement (observation) of the effects of this manipulation on behavior.
• The factors the researcher controls or manipulates are called the independent
variables. An independent variable must have at least two levels (also called
conditions). One level may be considered the “treatment” condition and a second
level the control (or comparison) condition.
• Often, more than two levels are used for additional comparisons between groups.
The measures used to observe the effect (if any) of the independent variables are
called dependent variables.
• One way to remember the distinction between these two types of variables is to
understand that the outcome (dependent variable) depends on the independent
variable.
