Understanding Psychology (10th Ed)

 
Module 5 
Conducting Psychological Research 
41
Experimental Research
The only way psychologists can establish cause-and-effect relationships through 
research is by carrying out an experiment. In a formal
experiment
,
the researcher 
investigates the relationship between two (or more) variables by deliberately chang-
ing one variable in a controlled situation and observing the effects of that change on 
other aspects of the situation. In an experiment, then, the conditions are created and 
controlled by the researcher, who deliberately makes a change in those conditions in 
order to observe the effects of that change.
The change that the researcher deliberately makes in an experiment is called the 
experimental manipulation
.
Experimental manipulations are used to detect relation-
ships between different variables.
Several steps are involved in carrying out an experiment, but the process 
typically begins with the development of one or more hypotheses for the experi-
ment to test. For example, Latané and Darley, in testing their theory of the diffu-
sion of responsibility in bystander behavior, developed this hypothesis: The higher 
the number of people who witness an emergency situation is, the less likely it is 
that any of them will help the victim. They then designed an experiment to test 
this hypothesis. 
Their 
fi rst step was to formulate an operational defi nition of the hypothesis 
by conceptualizing it in a way that could be tested. Latané and Darley had to take 
into account the fundamental principle of experimental research mentioned earlier: 
Experimenters must manipulate at least one variable in order to observe the effects 
of the manipulation on another variable while keeping other factors in the situa-
tion constant. However, the manipulation cannot be viewed by itself, in isolation; 
if a cause-and-effect relationship is to be established, the effects of the manipula-
tion must be compared with the effects of no manipulation or a different kind of 
manipulation.