Page 517 - Encyclopedia of Nursing Research

484 n STATISTICAl TeChnIQUeS

in health have been difficult to determine. variance (AnOVA) can accomplish the same
Although clear neurochemical and brain results, the t test continues to be used when
S pattern changes have been demonstrated appropriate as it is easy to present and to
with the use of meditation, prayer, and mys- understand.
tical experiences (hagerty, 2009; newberg & AnOVA is a parametric statistical test
newberg, 2005), the effect of interventions that measures differences between two or
such as distant intercessory prayer have not more mutually exclusive groups by calcu-
been well supported in research (masters, lating the ratio of between- to within-group
2007). In the studies of distant intercessory variance, called the F ratio. It is an extension
prayer, people who were being prayed for of the t test, which compares two groups. The
were also receiving medical treatment, so the independent variable(s) is categorical (mea-
effects of prayer could not be determined. sured at the nominal level). The dependent
Despite these challenges, when people variable must meet the assumptions of nor-
are considered from a holistic perspective, mal distribution and equal variance across
it is essential to include concepts and inter- the groups. A one-way AnOVA means that
ventions related to spirituality in studying there is only one independent variable (often
health and illness. called factor), a two-way AnOVA indicates
two independent variables, and an n-way
Carol D. Gaskamp AnOVA indicates that the number of inde-
Martha G. Meraviglia pendent variables is defined by n.
Analysis of covariance (AnCOVA) is a
statistical technique that combines AnOVA
with regression to measure the differences
StatiStical techniqueS among group means. AnCOVA has been used
in both experimental and nonexperimental
studies to “equate” the groups statistically.
There are many statistical techniques that When the groups differ on some variable,
are useful to nurses in the analysis of quanti- AnCOVA is used to reduce the impact of
tative research findings. Research questions that difference. Although AnCOVA has been
will provide the foundation for selecting the widely used for such statistical “equaliza-
statistical method. This entry reviews basic tion” of groups, there is controversy about
statistical techniques. The t test involves an such efforts, and careful consideration should
evaluation of means and distributions of two be given to the appropriateness of the manip-
groups. The t test, or Student’s t test, is named ulation. AnOVA and AnCOVA require that
after its inventor, William gosset, who pub- post hoc tests are used for pairwise compari-
lished under the pseudonym Student. gosset son of group means.
invented the t test as a more precise method An AnOVA may include more than one
of comparing groups. The t test reflects the dependent variable. Such an analysis usually
probability of getting a difference of a given is referred to as multivariate AnOVA and
magnitude in groups of a particular size allows the researcher to look for relationships
with a certain variability if random samples among dependent as well as independent
drawn from the same population were com- variables. When conducting a multivariate
pared. Three factors are included in the anal- AnOVA, the assumptions underlying the
ysis: difference between the group means, univariate model still apply; in addition,
size of each group, and variability of scores the dependent variable should have a “mul-
within the groups. The t tests are very useful tivariate normal distribution with the same
when two groups or two correlated measures variance covariance matrix in each group”
are being compared. Although analysis of (norusis, 1994, p. 58). The requirement that