Evidence-Based Practice for Nurses

be a minimum of two groups. To be considered a true experimental design,

three features must be present: randomization, control, and manipulation.

Essential Components of Experimental

Designs

Randomization in experimental designs is used in two ways. One way requires

researchers to randomly select subjects from the target population. The other

way is to randomly assign subjects to groups. Because random selection of

the sample usually is not possible in nursing research, random assignment to

groups is considered to be sufficient to meet the criterion of randomization

for an experiment.

The second component of experimental designs is control, which is related to

randomization. A control group, for comparison to the experimental group, is

one strategy researchers use to control for extraneous variables. In addition to

a control group, other ways researchers control for extraneous variables are by

exerting the highest level of control over the selection of subjects, the definitions

of the variables, and the environment in which the experiment is conducted.

Manipulation is the third essential component. Researchers must be able to

manipulate the independent variable (IV) for a design to be considered experi-

mental. This is accomplished by consistently administering the intervention.

True Experimental Designs

When creating an evidence-based practice (EBP), experimental designs are

most valued. When appraising quantitative research studies, you may see the

term randomized controlled trial (RCT), a term used to describe an experimen-

tal study that is conducted in healthcare settings. The RCT designation refers

to the fact that the study is “clinical” in nature rather than a specific type of

design. Regardless of the specific experimental design used, RCTs are char-

acterized by the following considerations: (1) they involve a large number of

subjects, often from diverse geographic areas; (2) there are strict guidelines for

including subjects in a study; (3) subjects are randomly assigned to either the

intervention or control group; (4) subjects in each group must be comparable

(equivalent) on key characteristics at baseline; (5) the intervention is consis-

tently implemented to all subjects in the experimental group following a very

Remember an experiment you conducted in your chemistry class. Identify the three essential

components of an experiment and tell how each was accounted for in your example.

CRITICAL THINKING EXERCISE 7-1

KEY TERM

experimental

designs: Designs

involving random

assignment

to groups and

manipulation of

the independent

variable

172 CHAPTER 7 Quantitative Designs: Using Numbers to Provide Evidence