To
define some concept of study in such a way that it can be observed and measured. For
example, "well being" might be measured by asking people to rate their overall
satisfaction with their life style, or "anti-social behaviour" might be measured
by frequency of arrest or criminal prosecution.
Operational definitions require that we first specify our
constructs; developing reliable and valid operations is the last step of specifying
constructs when we are designing our own studies. The science of psychology tries to
develop explanations of human behavior through objective observations. The procedures or
operations that we use to objectively measure a variable are known as its operational
definition. The operational definition gives the variable meaning within a particular
study. The features of a operational definition vary depending on the study design.
Operational Definitions Operationally Defined
Stuart C. Dodd, Ethel Shanas
The American Journal of Sociology, Vol. 48, No. 4 (Jan., 1943), pp. 482-491
Abstract: This paper attempts to meet the challenge of defining operational definitions
operationally. A definition is operational to the extent that it specifies the procedure
for identifying or generating the definiendum and finds high reliability for the
definition. The logical form of this definition, its gradational phrasing, the concepts of
"procedure" and "reliability," and the two types of operational
definitions are commented upon. The importance of reliability for scientific work is
stressed. Experimental procedures for measuring the utility, the reliability, the
validity, and the usage of any concepts defined are suggested and proposed as criteria for
the excellence of any sociological definition. - jstor.org
Historic Ideals Operationally Defined
Stuart C. Dodd
The Public Opinion Quarterly, Vol. 15, No. 3 (Autumn, 1951), pp. 547-556
Abstract: Moment formulas can be used as an aid in defining important human ideals and
values in measurable terms. Such classic ideals as "liberty, equality, and
fraternity" can be redefined as a moment of some one order. Eleven such conceptsare
analyzed here as examples of the exactness of meaning which the moments can yield. -
jstor.org
Expression profile of an operationally-defined neural stem cell clone.
Parker MA, Anderson JK, Corliss DA, Abraria VE, Sidman RL, Park KI, Teng YD, Cotanche
DA, Snyder EY.
Department of Otolaryngology, EN41, Children's Hospital-Boston, 300 Longwood Avenue,
Boston, MA 02115, USA. mark.parker@childrens.harvard.edu
Abstract: Neural stem cells (NSCs) are the most primordial and least committed cells of
the nervous system, the cells that exist before regional specification develops. Because
immunocytochemically-detectable markers that are sufficiently specific and sensitive to
define an NSC have not yet been fully defined, we have taken the strong view that, to be
termed a "stem cell" in the nervous system--in contrast to a
"progenitor" or "precursor" (whose lineage commitment is further
restricted)--a single neuroectodermally-derived cell must fulfill an operational
definition that is essentially similar to that used in hematopoiesis. In other words, it
must possess the following functional properties: (1) "Multipotency", i.e., the
ability to yield mature cells in all three fundamental neural lineages throughout the
nervous system--neurons (of all subtypes), astrocytes (of all types), oligodendrocytes--in
multiple regional and developmental contexts and in a region and developmental
stage-appropriate manner. (2) The ability to populate a developing region and/or
repopulate an ablated or degenerated region of the nervous system with appropriate cell
types. (3) The ability to be serially transplanted. (4) "Self-renewal", i.e.,
the ability to produce daughter cells (including new NSCs) with identical properties and
potential. Having identified a murine neural cell clone that fulfills this strict
operational definition--in contrast to other studies that used less rigorous or
non-operational criteria for defining an NSC (e.g., the "neurosphere" assay)--we
then examined, by comparing gene expression profiles, the relationship such a cell might
have to (a) a multipotent somatic stem cell from another organ system (the hematopoietic
stem cell [HSC]); (b) a pluripotent stem cell derived from the inner cell mass and hence
without organ assignment (an embryonic stem cell); (c) neural cells isolated and
maintained primarily as neurospheres but without having been subjected to the above
mentioned operational screen ("CNS-derived neurospheres"). ESCs, HSCs, and
operationally-defined NSCs--all of which have been identified not only by markers but by
functional assays in their respective systems and whose state of differentiation could be
synchronized--shared a large number of genes. Although, as expected, the most stem-like
genes were expressed by ESCs, NSCs and HSCs shared a number of genes. CNS-derived
neurospheres, on the other hand, expressed fewer "stem-like" genes held in
common by the other operationally-defined stem cell populations. Rather they displayed a
profile more consistent with differentiated neural cells. (Genes of neural identity were
shared with the NSC clone.) Interestingly, when the operationally-defined NSC clone was
cultured as a neurosphere (rather than in monolayer), its expression pattern shifted from
a "stem-like" pattern towards a more "differentiated" one, suggesting
that the neurosphere, without functional validation, may be a poor model for predicting
stem cell attributes because it consists of heterogeneous populations of cells, only a
small proportion of which are truly "stem-like". Furthermore, when operational
definitions are employed, a common set of stem-like genes does emerge across both
embryonic and somatic stem cells of various organ systems, including the nervous system. -
ncbi.nlm.nih.gov |