d. A researcher conducts an experiment in a
prison to determine the effect of a new
treatment program. During the experiment, a
large number of the inmates in the control
group are released on parole, although no
inmates in the experimental group are paroled
during the course of the study.
e. A researcher conducts an experiment in an
elementary school to determine the
effectiveness of an anti-drug education
program. As there are an equal number of
boys and girls in the school, the researcher
finds it easier to assign all the boys to the
experimental group and all the girls to the
treatment group
f. Instead of randomly selecting students to
participate in a study on campus, the
researcher asks students to volunteer. As a
result, only students who are interested in the
study participate.
g. A specific event takes place between the
first and second observations in a study that
may affect measurement.
8.Multiple-treatment interference
h. The researcher applies two different
treatments to the experimental group in a
research study.
9. Statistical regression
i. During a large-scale study in which crime
victims are interviewed, two interviewers
resign and must be replaced.
10. Experimental mortality
j. Prior to experiencing a treatment, subjects
in a study take a pretest. This sensitizes them
to the topic of the study. They may react
differently to the treatment than would
subjects who did not take the pretest first.
11. Differential selection
k. While interviewing subjects during an
experiment, the researcher does not treat the
subjects in the experimental and control group
identically.