(^106) Johns Hopkins Nursing Evidence-Based Practice: Model and Guidelines, Third Edition
A true experimental study has three distinctive features: randomization, control,
and manipulation. Randomization occurs when the researcher assigns subjects
to a control or experimental group randomly, similar to the roll of dice. This en-
sures that each potential subject who meets inclusion criteria has the same prob-
ability of selection for the experiment. That is, people in the experimental group
and in the control group generally will be identical, except for the introduction
of the experimental intervention or treatment. This is important because subjects
who take part in an experiment serve as representatives of the population that
may possibly benefit from the intervention.
Manipulation occurs when the researcher implements an intervention with at
least some of the subjects. In experimental research, an intervention is applied to
some subjects (the experimental group) and withheld from others (the control
group). The aspect that the researcher is trying to influence is the dependent vari-
able (e.g., the experience of low back pain). The experimental intervention is the
independent variable, or the action the researcher will take (e.g., application of
low-level heat therapy) to try to change the dependent variable.
Control usually refers to the introduction of a control or comparison group,
such as a group of subjects to which the experimental intervention is not applied.
The goal is to compare the effect of no intervention on the dependent variable
in the control group against the effect of the experimental intervention on the
dependent variable in the experimental group. Placebos, which may be given to
subjects in the control group, are used as a pseudo-intervention because they are
assumed by researchers to have no therapeutic value (Polit & Beck, 2017). When
placebos are used, they control for nonintervention effects such as attention be-
ing paid to subjects and subjects’ expectations of benefits and harms.
Example: Experimental Randomized Controlled Trial
Kiecolt-Glaser et al. (2014) reported on an experimental study investigating yoga’s
impact on inflammation, mood, and fatigue in breast cancer survivors. Following
randomization, participants were assigned to either 12 weeks of 90-minute hatha
yoga classes or a wait-list control. Participants assigned to wait-list control were
told to continue usual activities and refrain from beginning any yoga practice. After
final study assessment, wait-list controls were offered the yoga classes.