reasons that motivate the clinical usage of scales, questionnaires,
tests and rates can be diverse like help for diagnostic, support
for the frame of medical treatment, communication with other professionals,
and establishment of a populational point of reference.
"quantitative" urge that has ruled the health disciplines during
many years has converted the clinical measurement into an omnipresent
activity for the health practice and study. Based on this approach,
the legitimacy of the numerical data has been backed up by the physic
and objectifiable world from where it comes: blood pressure, volume
of cardiac ejection, body mass index. Nevertheless the health attention,
following its aspiration of providing answers to the complex human
dimensions from a growing multidisciplinarity, has forced to explore
"numerical statements" related to how much of an attribute is present
in one person. E.g.: social support perceived or quality of life
of a person.1
This kind of attributes is what is know as construct on its metric
analysis, meaning a hypothetic concept whose existence could never
be totally confirmed.1
is necessary to mention that patients and professionals use scales
constantly to communicate between each others, such as "I have a
headache" or "I have lost some weight". However, these measurements
must be considered as a process of evaluation and personal discernment2.
On the other hand, a measurement scale must be adapted to a set
of measurement axioms (model) to explain the quality of the ratio
between its variables and, if possible, the adjustment of the data
to the predictions of the model1.
Based on that, a scale of risk of pressure ulcer must be made of
variables interrelated and based on the model established (e.g.:
humidity, mobility.); the scores of that scale should be able to
predict the apparition of pressure ulcers.
metric properties are precisely the ones that differentiate a personal
judgment from a scale of measurement. However, depending on the
discipline, these properties will be studied in the field of psychometry,
econometrics, anthropometry, or where appropriate, in the field
of clinimetrics as the measurement of clinical phenomena
was firstly denominated by Alvan R. Feinstein2.
the process of clinimetric construction, the fundamental properties
demanded from a scale of measurement are the validity and the reliability,
in other words, the standardization of the contents and the standardization
as scale of measurement, respectively2.
The validity denotes the scientific utility of the scale; it denotes
to what extent, what has been measured approaches what was intended
On its side, the reliability points out the scientific utility of
the scale as a tool that shows its accuracy when measuring, putting
to the test its reproducibility in measurements performed later
or by different observers3.
a long and complex scientific process of elaboration of a clinical
scale, the exposition of which surpasses the content of the present
text, the scale is put at the health professional's disposal. He
will be the one in charge of deciding its use depending on the utility
perceived. Among these utilities that are found complementarily
it can be mentioned:
Help to diagnosis.
The clinical diagnosis is not determined by the test that only warns
about the risk of suffering the problem. It will be the professional
the one in charge of confirming or not its presence, using also
other clinical data taken into account as well. Great importance
is attached to the fact of knowing the capability of the methods
of diagnosis and prognosis used for the correct interpretation of
the results. In order to achieve it, it is fundamental to take into
account the sensitivity and specificity of a scale summed to the
expected prevalence of the problem in the population under study.
It must be remembered that the professional criterion is always
necessary to take a clinical decision; the scale should not make
the decision for the professional.
an explanatory remark, the concepts of sensitivity and specificity
should be defined. The sensitivity corresponds to the proportion
of cases (persons with a health problem) for which the test (scale)
has a positive result, that is to say, it points out the capability
of the scale to detect cases. On the other side, the specificity
is the proportion of no-cases for which the test result (scale)
is negative, in other words, it measures the capability to detect
Support for the
threshold of treatment. If the final aim for the administration
of a scale is to determine a therapeutic attitude, it will be necessary
to define in advance a threshold of treatment, that is to say, a
probability of suffering from the health problem previous to the
administration of the scale that will trigger the decision of treating
the patient. This threshold probability depends on the benefit of
treating persons having the problem, and also depends on the cost
of treating persons without the problem4.
If the benefit of intervention is high and the costs are low, the
threshold of treatment will be low as it happens in the case of
pressure ulcers, and vice versa. Again, the professional criterion
is revealed as determinant element to make clinical decisions beyond
the numeric value obtained after the administration of a scale.
with other professionals. The value obtained as a result of
the administration of a scale allows a synthesized and objective
communication, avoiding misunderstandings at the receptor side.
This utility is widely accepted for the communication between different
medical attendance levels. It must be mentioned that the value found
in a scale can and should be tinged with information of interest,
that might not have been caught in the scale, or that might be clinically
of a populational referent. Being the scale a tool of
measurement whose clinimetric properties are built by means of a
survey made on a concrete population, it is logical to think that
the value of each person under research is located relatively regarding
the value of the rest of the population.
In this way, a cut-point established in the scale can serve as criterion
for the distribution of resources or for derivation to another professional.
Among the mentioned resources we can point out the anti-slough mattresses
or the walkers; among the professionals to whom the patient will
be derived we can find the psychologists or the rehabilitator. At
this point, it is fundamental the role of the professional. He has
to attenuate the imperfections and the injustices of any criterion,
whose external nuances escape from its coverage.
Another important utility is found in the clinical research.
When finding objective and quantifiable values with a populational
referent, the scale becomes one of the most used methods of data
collection in the quantitative research. In this way, using a scale,
investigations to describe populational attributes can be developed;
those populational attributes can be compared with other populations
or within the same population mediated by a time interval, or they
can even be used to value the effectiveness of a certain intervention.
The scales of quality of life are the paradigm of this usage and
have made it possible to expand the analysis of effectiveness from
the point of view cost-utility. Nevertheless, some gaps from the
point of view of the economic and utilitarian models still need
to be solved.
As an added limitation
to the extrapolation of instruments developed in contexts where
populations with socio-cultural differences exist, the transcultural
adaptation to the environment where they are going to be used is
a mandatory step many times underestimated in the works of validation.
As a result of this negligence it is frequent to find a distortion
or damage in the validity of the scale content, and a variation
in its sensitivity and specificity.
must not be forgotten that there is not perfect test, and that any
score observed in a questionnaire is the result of adding a random
error to the real score1.
The disregard of the measurement error in the mentioned tests might
put the person under analysis at risk. The process of clinimetric
construction might, if it is done correctly, diminish this error
to the minimum. The critical evaluation of the instrument and the
analysis of the validation will contribute with enough factors to
determine its applicability.
it is necessary to remind that the indiscriminate usage of clinimetric
instruments will never replace the essential abilities needed for
the clinical interview nor the qualitative knowledge of the human
answer at the moment of bringing in a judgment. It is in synergy
with these abilities and knowledge, that the clinical deliberation
is increased and enriched.
1. Nunnally J, Bernstein
I. Teoría Psicométrica. 3ª Edición. México:
Mc Graw Hill, 1995.
2. Feinstein AR. Clinimetrics. New Haven:
Yale University Press, 1987
3. Streiner DL, Norman GR. Health
measurement scales. A practical guide to their development and use.
3rd Edition. New York: Oxford University Press, 2003.
J. Análisis de decisiones. Quaderns 12. Valencia: Instituto
Valenciano de Estudios en Salud Pública, 1997.