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EXPERIMENTAL RESEARCH
Researchers study variables, which are characteristics that take on different values
across people or things. Experimental research involves a study of the effect of the
systematic manipulation of one variable(s) on another variable. The manipulated
variable is called the experimental treatment or the independent variable. The
observed and measured variable is called the dependent variable. For example,
assume a university researcher wanted to investigate the effect of providing online
feedback to students immediately following course examinations. Using two sections of economics taught by the same professor, the researcher using a random
procedure would select one section to receive immediate online feedback about
their performance on test questions; the other section would receive feedback during their next class session (independent variables). The researcher would compare the two sections’ exam scores and their fi nal grades in the course (dependent
variables). If test scores and fi nal grades were higher than could be accounted for
by chance in the section receiving online feedback, the researcher could tentatively
conclude that there is evidence the online feedback (treatment or independent
variable) contributed to greater learning than the in-class feedback.
In experiments, you seek to control all other variables that might infl uence the
dependent variable. In the foregoing example, the researcher would attempt to
make sure that both groups had the same instructor; that both sections met at the
same time of day but on different days; that lecture notes, readings, and exams
were the same; and so forth. The researcher might also check the ability level
and background of the students in the two sections to make sure one section was
not superior or better prepared than the other.
To have a “true” experiment, researchers must use a random process such as a
coin toss to assign available subjects to the experimental treatments. With random
assignment, each subject has an equal and independent chance of being assigned to
any group; thus, the assignment is independent of the researcher’s personal judgment
or the characteristics of the subjects themselves. Sometimes, however, researchers
cannot randomly assign subjects to experimental treatments for a study. Instead,
as in the preceding example, the experimenter must use already assembled groups
such as classes. In this case, the research is called quasi-experimental. We discuss
experimental research more thoroughly in Chapters 10 and 11.