Evidence-Based Practice for Nurses

True/False

1. All experiments must include a minimum of three groups of subjects.


2. The Solomon four-group design is more effective at controlling for the threat of testing
   than is the two-group pretest-posttest design.


3. In a factorial design, only one group of subjects is required because they act as their own
   control.


4. Patients who are not in the intervention group must receive the usual standard of care.

TEST YOUR KNOWLEDGE 7-1

How did you do? 1. F; 2. T; 3. F; 4. T

Quasi-experimental designs are similar to experimental designs in that they
involve manipulation of the IV, but they do not meet one of the other essen-
tial components of experimental designs (Campbell & Stanley, 1966; Cook &
Campbell, 1979). They either lack randomization or a control group, which
makes claims of cause and effect weaker than in experimental designs. Because
of this, studies using quasi-experimental designs are ranked lower as sources
of evidence than are studies using experimental designs. However, there are
many situations involving the study of human health when it is not feasible or
ethical to conduct an experiment. Therefore, quasi-experimental designs serve
an important function in providing beginning evidence of causality. There are
three commonly used quasi-experimental designs: (1) nonequivalent control
group pretest-posttest, (2) one-group time series, and (3) preexperimental
designs (see Table 7-3).

Nonequivalent Control Group

Pretest-Posttest Designs

The nonequivalent control group pretest-posttest design differs from the
classic experimental design in that researchers are unable to randomly as-
sign subjects to groups. Because researchers are unable to randomize in these

7.2 Quasi-Experimental Designs

At the end of this section, you will be able to:

‹ Discuss the key difference between quasi-experimental and experimental designs

‹ Identify major quasi-experimental designs

‹ Discuss the advantages and disadvantages of various quasi-experimental designs

KEY TERMS

quasi-experimental

designs: Research

designs involving

the manipulation

of the independent

variable but lacking

either random

assignment to

groups or a control

group

nonequivalent

control group

pretest-posttest

design: A quasi-

experimental

design where

two groups are

measured before

and after an

intervention

7.2 Quasi-Experimental Designs 177