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Author Instructions |
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Glossary of Methodologic Terms
B
BEFORE-AFTER TRIAL. Investigation of therapeutic
alternatives in which individuals of one period and under one treatment
are compared with individuals at a subsequent time, treated in a
different fashion. If the disorder is not fatal and the "before"
treatment is not curative, the same individuals may be studied in the
before and after periods, strengthening the design through increased
group comparability for the two periods. See also CROSSOVER
TRIAL.
BLIND or BLINDED. Masked.
Unaware. The term may be modified according to the purpose of the
blinding. For example, clinicians or patients can be blind to the
treatments that patients are receiving and observers can be blind to
each other's assessments, making their observations uninfluenced by
one another (see also DOUBLE-BLIND). To avoid confusion, the term MASKED is preferred in studies in which vision loss of patients is an
outcome of interest.
C
CASE-CONTROL STUDY
(CASE-REFERENT OR CASE-COMPARISON STUDY). Study generally used to
test possible causes of a disease or disorder, in which individuals who
have a designated disorder are compared with individuals who do not
have the disorder with respect to previous current exposure to a
putative causal factor. For example, persons with hepatic cancer
(cases) are compared with persons without hepatic cancer (controls) and
history of hepatitis B is determined for the two groups. A CASE-CONTROL
STUDY is often referred to as a RETROSPECTIVE STUDY (even if patients
are recruited prospectively) because the logic of the design leads from
effect to cause.
CASE SERIES. A series
of patients with a defined disorder. The term is usually used to
describe a study reporting on a consecutive collection of patients
treated in a similar manner, without a concurrent control group. For
example, a surgeon might describe the characteristics of and outcomes
for 100 consecutive patients with cerebral ischemia who received a
revascularization procedure. See also CONSECUTIVE
SAMPLE.
COHORT. A group of persons with
a common characteristic or set of characteristics. Typically, the group
is followed for a specified period to determine the incidence of a
disorder or complications of an established disorder (that is,
prognosis), as in COHORT ANALYTIC STUDY (prospective study) (see also INCEPTION COHORT).
COHORT ANALYTIC STUDY.
Prospective investigation of the factors that might cause a
disorder in which a cohort of individuals who do not have evidence of
an outcome of interest but who are exposed to the putative cause are
compared with a concurrent cohort who are also free of the outcome but
not exposed to the putative cause. Both cohorts are then followed to
compare the incidence of the outcome of
interest.
CONFOUNDER, CONFOUNDING VARIABLE.
A factor that distorts the true relationship of the study
variables of central interest by virtue of being related to the outcome
of interest but extraneous to the study question and unequally
distributed among the groups being compared. For example, age might
confound a study of the effect of a toxin on longevity if individuals
exposed to the toxin were older than those not
exposed.
CONSECUTIVE SAMPLE. Sample in
which the units are chosen on a strict "first come, first chosen"
basis. All individuals who are eligible should be included as they are
seen.
CONVENIENCE SAMPLE. Individuals or
groups selected at the convenience of the investigator or primarily
because they were available at a convenient time or
place.
COST-BENEFIT ANALYSIS. A form of
economic assessment, usually from society's perspective, in which the
costs of medical care are compared with the economic benefits of the
care, with both costs and benefits expressed in units of currency. The
benefits typically include reductions in future health care costs and
increased earnings due to the improved health of those receiving the
care.
COST-EFFECTIVENESS ANALYSIS. An
economic evaluation in which alternative programs, services, or
interventions are compared in terms of the cost per unit of clinical
effect (for example, cost per life saved, cost per millimeter of
mercury of blood pressure lowered, or cost per quality-adjusted
life-year gained). The last form of measuring outcomes (and equivalents
such as "healthy days of life gained") gives rise to what is also
referred to as COST-UTILITY
ANALYSIS.
COST-UTILITY ANALYSIS. See
COST-EFFECTIVENESS ANALYSIS.
CRITERION
STANDARD. Preferred term to "gold standard." A method having
established or widely accepted accuracy for determining a diagnosis,
providing a standard to which a new screening or diagnostic test can be
compared. The method need not be a single or simple procedure but could
include follow-up of patients to observe the evolution of their
conditions or the consensus of an expert panel of clinicians, as is
frequently used in the study of psychiatric conditions. CRITERION
STANDARD can also be used in studies of the quality of care to indicate
a level of performance, agreed to by experts or peers, to which the
performance of individual practitioners or institutions can be
compared.
CROSSOVER TRIAL. A method of
comparing two or more treatments or interventions in which subjects or
patients, on completion of the course of one treatment, are switched to
another. Typically, allocation to the first treatment is by random
process. Participants' performance in one period is used to judge
their performance in others, usually reducing variability. See also
BEFORE-AFTER TRIAL.
D
DATA SET. Raw data
gathered by investigators.
DOUBLE-BLIND or
DOUBLE-MASK. (1) Neither the subject nor the study staff (those
responsible for patient treatment and data collection) are aware of the
group or intervention to which the subject has been assigned. (2) Any
condition in which two different groups of persons are purposely denied
access to information in order to keep that information from
influencing some measurement, observation, or
process.
E
ECONOMIC EVALUATION.
Comparative analysis of alternative courses of action in terms of both
their costs and consequences.
END
POINT. See OUTCOMES.
G
GOLD
STANDARD. See CRITERION
STANDARD.
I
INCEPTION COHORT. A designated
group of persons, assembled at a common time early in the development
of a specific clinical disorder (for example, at the time of first
exposure to the putative cause or at the time of initial diagnosis),
who are followed thereafter (see also
COHORT).
L
LIKELIHOOD RATIO. For a
screening or diagnostic test (including clinical signs or symptoms),
expresses the relative odds that a given test result would be expected
in a patient with (as opposed to one without) a disorder of
interest.
M
MASKED. See
BLIND.
MATCHING. The deliberate process
of making a study group and a comparison group comparable with respect
to factors that are extraneous to the purpose of the investigation but
that might interfere with the interpretation of the study's findings
(for example, in case-control studies, individual cases might be
matched or paired with a specific control on the basis of comparable
age, gender, clinical features, or a
combination).
N
NONRANDOMIZED CONTROL
TRIAL. Experiment in which assignment of patients to the
intervention groups is at the convenience of the investigator or
according to a preset plan that does not conform to the definition of
RANDOM. See also RANDOMIZED CONTROL
TRIAL.
O
OUTCOMES. All possible changes in
health status that may occur in following subjects or that may stem
from exposure to a causal factor or from preventive or therapeutic
interventions. The narrower term END POINTS refers to health events
that lead to completion or termination of follow-up of an individual in
a trial or cohort study, for example, death or major morbidity,
particularly related to the study
question.
P
PRIMARY CARE. Medical care
provided by the clinician of first contact for the patient. Typically,
the primary care physician is a general practitioner, family
practitioner, primary care internist, or primary care pediatrician.
Primary care may also be administered by health professionals other
than physicans, notably, specially trained nurses (nurse practitioners)
and physician assistants. Usually, a general practitioner, family
practitoner, nurse practitioner, or physician assistant provides only
primary care services but a person with specialty qualifications may
provide primary care, alone or in combination with referral services
(see also REFERRED CARE). Thus, it is the nature of the contact (first
compared with referred) that determines the care designation rather
than the qualifications of the
practitioner.
PRIMARY CARE CENTER, PRIMARY
CARE SETTING. Medical care facility that offers first-contact
health care only. Patients requiring specialized medical care are
referred elsewhere. Some primary care centers provide a mixture of
primary and referred care. Thus it is the nature of the service
provided (first contact) rather than the setting per se that
distinguishes primary from more advanced levels of care. See also
PRIMARY CARE, REFERRED CARE, TERTIARY CARE CENTER.
PROSPECTIVE STUDY. See COHORT
and COHORT ANALYTIC STUDY.
R
RANDOM.
Governed by a formal chance process in which the occurrence of previous
events is of no value in predicting future events. The probability of
assignment of, for example, a given subject to a specified treatment
group is fixed and constant (typically 0.50) but the subject's actual
assignment cannot be known until it
occurs.
RANDOM SAMPLE. A sample derived
by selecting sampling units (for example, individual patients) such
that each unit has an independent and fixed (generally equal) chance of
selection. Whether a given unit is selected is determined by chance
(for example, by a table of randomly ordered
numbers).
RANDOMIZATION, RANDOM
ALLOCATION. Allocation of individuals to groups by chance, usually
done with the aid of a table of random numbers. Not to be confused with
systematic allocation (for example, on even and odd days of the month)
or allocation at the convenience or discretion of the
investigator.
RANDOMIZED TRIAL
(RANDOMIZED CONTROL[LED] TRIAL, RANDOMIZED CLINICAL TRIAL,
RCT). Experiment in which individuals are randomly allocated to
receive or not receive an experimental preventive, therapeutic, or
diagnostic procedure and then followed to determine the effect of the
intervention.
REFERRED CARE. Medical
care provided to a patient when referred by one health professional to
another with more specialized qualifications or interests. There are
two levels of referred care: secondary and tertiary. Secondary care is
usually provided by a broadly skilled specialist such as a general
surgeon, general internist, or obstetrician. Tertiary care is provided
on referral of a patient to a subspecialist, such as an orthopedic
surgeon, neurologist, or neonatologist. See also TERTIARY CARE
CENTER.
RETROSPECTIVE STUDY. See
CASE-CONTROL STUDY.
S
SECONDARY CARE. See
REFERRED CARE.
SENSITIVITY. The
sensitivity of a diagnostic or screening test is the proportion of
people who truly have a designated disorder who are so identified by
the test. The test may consist of or include clinical
observations.
SEQUENTIAL SAMPLE. See
CONSECUTIVE SAMPLE.
SPECIFICITY. The
specificity of a diagnostic or screening test is the proportion of
people who are truly free of a designated disorder who are so
identified by the test. The test may consist of or include clinical
observations.
SURVEY. Observational or
descriptive, nonexperimental study in which individuals are
systematically examined for the absence or presence (or degree of
presence) of characteristics of
interest.
T
TERTIARY CARE. See REFERRED
CARE.
TERTIARY CARE CENTER. A tertiary
care center is a medical facility that receives referrals from both
primary and secondary care levels and usually offers tests, treatments,
and procedures that are not available elsewhere. Most tertiary care
centers offer a mixture of primary, secondary, and tertiary care
services so that it is the specific level of service rendered rather
than the facility that determines the designation of care in a given
study. See also REFERRED CARE.
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