Page 312 - Encyclopedia of Nursing Research

MEASUREMENT AND SCALES n 279

and categorization, using a common concep- unorderable categories. For example, catego-
tual perspective. Ambiguity, confusion, and rizing persons in a study as either female or
disagreement will surround the meaning of male is measurement on the nominal mea- M
any measurement when it is undefined. The surement scale.
measurement relevancy can be determined In ordinal-scale measurement, rules are
only when an explicit or implicit theory struc- used to assign rank order on a particular
tures the meaning of the phenomenon to be attribute that characterizes a person, object,
studied. “Theory not only determines what or event. Ordinal-scale measurement may be
attributes or aspects are measured but also regarded as the rank ordering of objects into
how they are to be measured” (Pedhazur & hierarchical quantitative categories accord-
Schmelkin, 1991, p. 16). Qualitative assess- ing to relative amounts of the attribute stud-
ments apply measurement principles by ied. The categorization of heart murmurs in
providing meaning and interpretation of grades from 1 through 6 is an example. In this
qualitative data through description and ordinal measure, a Grade 1 murmur is less
categorization of phenomena. Thus, mea- intense than a Grade 2, a Grade 2 less intense
surement may not result in scores per se but than a Grade 3, and so forth. The rankings in
may categorize phenomena into meaningful ordinal-level measurement merely mean that
and interpretable attributes. Therefore, mea- the ranking of 1 (for first) has ranked higher
surement is also basic to qualitative analysis than 2 (for second) and so on. Rankings do
(Strickland, 1993b). not imply that the categories are equally
Measurement is a crucial part of all nurs- spaced nor that the intervals between rank
ing settings. Nurses depend on measuring categories are equal.
instruments to determine the amount or kind Interval-scale measurement is a form
of attributes of patients and use the results of of continuous measurement and implies
measurements such as laboratory and physi- equal numerical distances between adjacent
cal examination results to determine patient scores that represent equal amounts with
needs and their plan of care. Nurse research- respect to the attribute that is the focus of
ers use a large array of physiological, clinical measurement. Therefore, numbers assigned
laboratory, observational, and questionnaire in interval-scale measurement represent an
measures to study phenomena of interest. attribute’s placement in one of a set of mutu-
Nurse educators depend on measurement ally exclusive, exhaustive categories that can
instruments and test scores to help determine be ordered and are equally spaced in terms of
a student’s mastery. Measurement is central the magnitude of the attribute under consid-
to all that nurses do. We cannot understand eration. However, the absolute amount of the
or “study well what we cannot measure well” attribute is not known for a particular object
(Strickland, 1993a, p. 4). because the zero point is arbitrary in an
The rules used for assigning numbers interval scale. The measurement of temper-
to objects to represent the amount or kind ature is a good example of an interval-level
of an attribute studied have been catego- measure because there is no true zero point.
rized as nominal, ordinal, interval, and ratio. For example, the zero point is different based
These types of measurement scales are com- on whether the Fahrenheit or Centigrade
mon in nursing. Measurements that result measurement approach is used, and one can-
in nominal-scale data place attributes into not say that an object with a temperature of
defined categories according to a specified 0°F or 0°C has no temperature at all. Ratio-
property. Numbers assigned to nominal- level measures provide the same informa-
level data have no hierarchical meaning but tion as interval-level measures; in addition,
represent an object’s membership in one of they have absolute zero points for which zero
a set of mutually exclusive, exhaustive, and actually represent absence of the attribute