Page 389 - Encyclopedia of Nursing Research

356 n OBSeRVATIONAL ReSeARCH DeSIGN

myriad sources of bias that can invalidate comparative design is referred to as a cohort
naturally occurring events, rigorous designs study. Participants are measured or catego-
O and methods are required to minimize bias. rized on the basis of the independent variable
Observational designs should not be con- and are followed over time for observation
fused with observational methods of data of the dependent variable. In a cohort study,
collection. it is established at the outset that subjects
Observational designs are used when have not already exhibited the outcomes of
there is not enough knowledge about a phe- interest (dependent variable). Thus, the time
nomenon to manipulate it experimentally. sequencing of events can be established. In
Sometimes research involving human partic- other words, it can be demonstrated that the
ipants is restricted to observational designs independent variable preceded the occur-
because of the nature of the phenomenon; rence of the dependent variable.
that is, experimental research is precluded Another type of longitudinal, compar-
for ethical reasons. ative design is a case–comparison study,
Observational designs include quantita- sometimes referred to as a case–control
tive, descriptive studies as well as analytical study. In this design, the flow is the opposite
studies that are designed to test hypotheses. of a cohort study. Participants are selected
Descriptive, observational studies provide and categorized on the basis of the depen-
a basis for further study by describing and dent variable (the outcome of interest). The
exploring relationships between variables, purpose of the study is to test hypothe-
informing the planning of health services, ses about factors in the past (independent
and describing clinical practice for individ- variables) that may explain the outcome.
ual clients or groups of clients. In contrast, Although case–comparison designs are not
analytic research is designed to test specific prevalent in the nursing research literature,
hypotheses to draw conclusions about the they have great potential for studies of out-
impact of an independent variable or set of comes that occur infrequently. Furthermore,
variables on an outcome, the dependent var- this design is very efficient because it is pos-
iable under scrutiny. Observational designs sible to achieve greater statistical power with
are classified as longitudinal or cross sec- a smaller sample size than in other types of
tional. In a cross-sectional study, all the mea- observational designs.
surements relate to one point in time; in the Longitudinal comparative designs are
longitudinal approach, measurements relate also classified according to the time perspec-
to at least two points in time. tive of the events under study in relation to
A cross-sectional study, sometimes the investigator’s position in time. A study is
referred to as a correlational study, is con- retrospective if, relative to when the inves-
ducted to establish that a relationship exists tigator begins the study, the events under
between variables. The term correlational investigation have already taken place. A
refers to a method of analysis rather than a study is prospective if the outcomes that are
feature of the design itself. Cross-sectional being investigated have not yet taken place
studies are useful if the independent vari- when the study is initiated. Various hybrid
able is an enduring personal characteristic, designs are also possible, referred to as ambi-
for instance, gender or blood type. Cross- directional studies; they combine features
sectional studies are also useful for exploring of both time perspectives (Aschengrau &
associations between and among variables. Seage, 2008).
Longitudinal comparative designs are As in experimental research, observa-
usually undertaken to explain the rela- tional research designs and methods are
tionship between an independent variable selected with the aim of minimizing bias. Bias
and an outcome. One type of longitudinal, refers to distortion in the result of a study. A