Readings and Overview
Week 6 Activity
Week 6 Assignment
Objective 2: Identify the following designs used
in nursing research: Descriptive, correlational, quasi-experimental, and
experimental study designs. (Objective 3 covered later in Topic 2.)
What types of research designs are used
in nursing research?
Research designs can be divided in to two broad categories:
research – In this category the researcher observes the phenomena as
they occur naturally and does not intervene in any way. Types of designs
in this category include:
- Correlational research
- Experimental research -
In this category the researcher plays an active role by manipulating the
independent variable (IV) in the form of delivery of a treatment or
intervention. Experimental research is conducted to examine cause
and effect. Two types of design fall into this category:
research –The following three elements must be present in a
study for it to be considered an experimental design.
- Random assignment
of subjects to the control/comparison group or the experimental group
- Manipulation of the
IV by the researcher
- Control of the research
setting and situation by the researcher
research – Because of the ethical nature of conducting studies with
human subjects, often an experimental design is not feasible.
The quasi-experimental design must include:
- Manipulation of the
IV by the researcher,
but it may lack:
- A control group.
However, in quasi-experimental design there is a nonequivalent comparison
group. It is called a comparison group, instead of control
group because members of the group were not randomly assigned to
experimental or control conditions. Thus, there is no assurance that
subject characteristics are equally and randomly distributed between
groups, and this introduces a potential source of error.
- Control of the
research setting and situation.
Types of Research Designs
- Typical Descriptive
Design: Examines characteristics of a single sample (explores aspects
of phenomena of interest).
Descriptive Design: Compares two or more groups that occur naturally in
a setting (explores for differences).
- Case Study:
Intensive exploration of a single unit of study (a person, family,
group, community, or institution).
descriptive (not covered in the book): Studies a sample of individuals
over time to examine patterns of change, growth, or trends across time.
Correlational Design: Describes the relationship among variables in a
Correlational (not covered in the book): Because we know reality in the
world is multicausal, that is, there are many factors that influence an
outcome, most correlational studies now are multifactorial and examine
correlations between more than 2 variables simultaneously.
- Predictive Correlational:
Attempts to explore what factors predict (have an influence on) another
variable. Because this design explores causality, the term independent
variable is used to describe the predictor variables that are
thought to predict the outcome variables (often called the dependent
variable). (Please note: This use of the terminology independent
variable and dependent variable is confusing because the
terms have a much more exact meaning in quasi and experimental
These studies can be done prospectively (with all data
collected at the same time), but this is not a strong design. A strong design
for a predictive correlational study collects data on the independent
(predictor) variables at one point in time then examines the extent to
which these variables relate to (predict) an outcome (dependent variable)
at another point in time.
Nursing students are enrolled in a study to evaluate the risk factors
associated with the development of cardiovascular disease. The students
complete cardiovascular risk factor questionnaires when the study begins then
are followed at regular intervals for the next 30 years. Data collected during
the follow-up visits includes current information about risk factors and
information about the presence of cardiovascular disease (hypertension,
hypercholesterolemia, MI, angina, stroke, etc). This allows the researchers
to look back at the data and see if those students who reported cigarette
smoking or a lack of physical activity had a higher incidence of
cardiovascular diseases. If they do, then the risk factor (independent
predictor variable) can be said to predict the outcome (dependent
variable) of cardiovascular disease
- Model Testing
Design: This design is similar to a predictive correlational design but
is testing a hypothesized causal model. It requires a larger sample
size and very tight measurement of variables.
- Similar to
experimental design, but does not have the same level of control (e.g.,
are not able to control as many threats as possible). Aspects that
might not be controlled are:
- Not having a
control group to which to compare results
- Not randomly
assigning participants to control or experimental group
- Not having control
over the intervention (e.g., using an intervention that is in place in
- Many different
quasi-experimental designs exist. You are
responsible for understanding the concepts that make such a design
- You do not need to
memorize each of the many different types of quasi-experimental
- Provides the best
method possible to examine a cause and effect situation. Provides the
greatest amount of control for examining causality. Tries to reduce or
eliminate (almost impossible) all factors that influence the dependent
(outcome) variable other than the intervention (the independent variable).
This is done by:
- Sample selection
for homogeneity (which we will discuss later)
- Random sampling
(randomly enrolling individuals from the population is not usually
possible in health studies—we usually have a convenience sample.
- Random assignment
of participants into control and experimental group (so every eligible
person has an equal chance of being assigned to the
experimental/intervention or the control group—thereby theoretically
evenly distributing into each group any characteristics of the sample
that might have an impact on the outcome variable)
- Controlling the
intervention as tightly as possible and controlling as many other
extraneous variables as possible.
- Experimental designs
are varied. You are responsible for understanding
the standard randomized pretest post-test design with control and
experimental group and randomized clinical trials. (You may
skip factorial designs.)
- Additional Points
versus Prospective -
- Descriptive and
correlational studies can be retrospective (this means that the
data being analyzed was either collected in the past as in chart data
or that the data collection focuses on the past. Example: Studying
women’s dietary practices and levels of physical activity after they
have completed a Phase II cardiac rehabilitation program.
- Prospective means
that the data was collected after the study was designed and focuses
on the here and now. Example: Studying women’s dietary practices and
levels of physical activity while they are in the process of
initiating lifestyle changes during cardiac rehabilitation.
- Almost any design can be longitudinal.
- This means that
data were collected over time, not just once or twice.
longitudinal studies collect data from subjects about phenomena over
weeks, months, or years. Many developmental studies are descriptive
longitudinal studies that continue for the lifetime of the individuals
- These data are used
descriptively and also are used for many different correlational, and
especially multifactorial correlational, analyses to explore factors
that influence positive and problematic developmental outcomes.
- Experimental and
quasi-experimental studies can collect outcome data longitudinally to
determine whether the experiment (intervention, independent variable)
has a long-term effect.
Remember, a study can use a combination of designs and most sophisticated