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GLOSARIO DE TÉRMINOS
A B C
D E F G H I
J
K L M N O P
Q R S T
U V W X Y Z
A
age-adjusted mortality rate: A mortality rate statistically modified
to eliminate the effect of different age distributions in the different
populations.
agent: A factor, such as a microorganism,
chemical substance, or form of radiation, whose presence, excessive presence, or
(in deficiency diseases) relative absence is essential for the occurrence of a
disease.
age-specific mortality rate: A mortality
rate limited to a particular age group. The numerator is the number of deaths in
that age group; the denominator is the number of persons in that age group in
the population.
analytic epidemiology: The aspect of
epidemiology concerned with the search for health-related causes and effects.
Uses comparison groups, which provide baseline data, to quantify the association
between exposures and outcomes, and test hypotheses about causal relationships.
analytic study: A comparative study
intended to identify and quantify associations, test hypotheses, and identify
causes. Two common types are cohort study and case-control study.
applied epidemiology: The application or
practice of epidemiology to address public health issues.
association: Statistical relationship
between two or more events, characteristics, or other variables.
attributable proportion: A measure of the
public health impact of a causative factor; proportion of a disease in a group
that is exposed to a particular factor which can be attributed to their exposure
to that factor.
B
bias: Deviation of results or inferences
from the truth, or processes leading to such systematic deviation. Any trend in
the collection, analysis, interpretation, publication, or review of data that
can lead to conclusions that are systematically different from the truth.
C
case: In epidemiology, a countable
instance in the population or study group of a particular disease, health
disorder, or condition under investigation. Sometimes, an individual with the
particular disease.
case-control study: A type of
observational analytic study. Enrollment into the study is based on presence
("case'') or absence ("control'') of disease. Characteristics such as previous
exposure are then compared between cases and controls.
case definition: A set of standard
criteria for deciding whether a person has a particular disease or
health-related condition, by specifying clinical criteria and limitations on
time, place, and person.
case-fatality rate: The proportion of
persons with a particular condition (cases) who die from that condition. The
denominator is the number of incident cases; the numerator is the number of
cause-specific deaths among those cases.
cause of disease: A factor
(characteristic, behavior, event, etc.) that directly influences the occurrence
of disease. A reduction of the factor in the population should lead to a
reduction in the occurrence of disease.
cause-specific mortality rate: The
mortality rate from a specified cause for a population. The numerator is the
number of deaths attributed to a specific cause during a specified time
interval; the denominator is the size of the population at the midpoint of the
time interval.
census: The enumeration of an entire
population, usually with details being recorded on residence, age, sex,
occupation, ethnic group, marital status, birth history, and relationship to
head of household.
class interval: A span of values of a
continuous variable which are grouped into a single category for a frequency
distribution of that variable.
cluster: An aggregation of cases of a
disease or other health-related condition, particularly cancer and birth
defects, which are closely grouped in time and place. The number of cases may or
may not exceed the expected number; frequently the expected number is not known.
cohort: A well-defined group of people
who have had a common experience or exposure, who are then followed up for the
incidence of new diseases or events, as in a cohort or prospective study. A
group of people born during a particular period or year is called a birth
cohort.
cohort study: A type of observational
analytic study. Enrollment into the study is based on exposure characteristics
or membership in a group. Disease, death, or other health-related outcomes are
then ascertained and compared.
confidence interval: A range of values
for a variable of interest, e.g., a rate, constructed so that this range has a
specified probability of including the true value of the variable. The specified
probability is called the confidence level, and the end points of the confidence
interval are called the confidence limits.
confidence limit: The minimum or maximum
value of a confidence interval.
contingency table: A two-variable table
with cross-tabulated data.
control: In a case-control study,
comparison group of persons without disease.
crude mortality rate: The mortality rate
from all causes of death for a population.
cumulative frequency: In a frequency
distribution, the number or proportion of cases or events with a particular
value or in a particular class interval, plus the total number or proportion of
cases or events with smaller values of the variable.
cumulative frequency curve: A plot of the
cumulative frequency rather than the actual frequency for each class interval of
a variable. This type of graph is useful for identifying medians, quartiles, and
other percentiles.
D
demographic information: The "person''
characteristics--age, sex, race, and occupation--of descriptive epidemiology
used to characterize the populations at risk.
denominator: The lower portion of a
fraction used to calculate a rate or ratio. In a rate, the denominator is
usually the population (or population experience, as in person-years, etc.) at
risk.
dependent variable: In a statistical
analysis, the outcome variable(s) or the variable(s) whose values are a function
of other variable(s) (called independent variable(s) in the relationship under
study).
descriptive epidemiology: The aspect of
epidemiology concerned with organizing and summarizing health-related data
according to time, place, and person.
determinant: Any factor, whether event,
characteristic, or other definable entity, that brings about change in a health
condition, or in other defined characteristics.
distribution: In epidemiology, the
frequency and pattern of health-related characteristics and events in a
population. In statistics, the observed or theoretical frequency of values of a
variable.
E
endemic disease: The constant presence of
a disease or infectious agent within a given geographic area or population
group; may also refer to the usual prevalence of a given disease within such
area or group.
environmental factor: An extrinsic factor
(geology, climate, insects, sanitation, health services, etc.) which affects the
agent and the opportunity for exposure.
epidemic: The occurrence of more cases of
disease than expected in a given area or among a specific group of people over a
particular period of time.
epidemic curve: A histogram that shows
the course of a disease outbreak or epidemic by plotting the number of cases by
time of onset.
epidemic period: A time period when the
number of cases of disease reported is greater than expected.
epidemiologic triad: The traditional
model of infectious disease causation. includes three components: an external
agent, a susceptible host, and an environment that brings the host and agent
together, so that disease occurs.
epidemiology: The study of the
distribution and determinants of health-related states or events in specified
populations, and the application of this study to the control of health
problems.
evaluation: A process that attempts to
determine as systematically and objectively as possible the relevance,
effectiveness, and impact of activities in the light of their objectives.
experimental study: A study in which the
investigator specifies the exposure category for each individual (clinical
trial) or community (community trial), then follows the individuals or community
to detect the effects of the exposure.
exposed (group): A group whose members
have been exposed to a supposed cause of disease or health state of interest, or
possess a characteristic that is a determinant of the health outcome of
interest.
F
frequency distribution: A complete
summary of the frequencies of the values or categories of a variable; often
displayed in a two column table: the left column lists the individual values or
categories, the right column indicates the number of observations in each
category.
G
graph: A way to show quantitative data
visually, using a system of coordinates.
H
health: A state of complete physical,
mental, and social well-being and not merely the absence of disease or
infirmity.
health indicator: A measure that
reflects, or indicates, the state of health of persons in a defined population,
e.g., the infant mortality rate.
health information system: A combination
of health statistics from various sources, used to derive information about
health status, health care, provision and use of services, and impact on health.
high-risk group: A group in the community
with an elevated risk of disease.
hyperendemic disease: A disease that is
constantly present at a high incidence and/or prevalence rate.
hypothesis: A supposition, arrived at
from observation or reflection, that leads to refutable predictions. Any
conjecture cast in a form that will allow it to be tested and refuted.
hypothesis, null: The first step in
testing for statistical significance in which it is assumed that the exposure is
not related to disease.
hypothesis, alternative: The hypothesis,
to be adopted if the null hypothesis proves implausible, in which exposure is
associated with disease.
I
immunity, active: Resistance developed in
response to stimulus by an antigen (infecting agent or vaccine) and usually
characterized by the presence of antibody produced by the host.
immunity, herd: The resistance of a group
to invasion and spread of an infectious agent, based on the resistance to
infection of a high proportion of individual members of the group. The
resistance is a product of the number susceptible and the probability that those
who are susceptible will come into contact with an infected person.
immunity, passive: Immunity conferred by
an antibody produced in another host and acquired naturally by an infant from
its mother or artificially by administration of an antibody-containing
preparation (antiserum or immune globulin).
incidence rate: A measure of the
frequency with which an event, such as a new case of illness, occurs in a
population over a period of time. The denominator is the population at risk; the
numerator is the number of new cases occurring during a given time period.
independent variable: An exposure, risk
factor, or other characteristic being observed or measured that is hypothesized
to influence an event or manifestation (the dependent variable).
individual data: Data that have not been
put into a frequency distribution or rank ordered.
inference, statistical: In statistics,
the development of generalizations from sample data, usually with calculated
degrees of uncertainty.
interquartile range: The central portion
of a distribution, calculated as the difference between the third quartile and
the first quartile; this range includes about one-half of the observations in
the set, leaving one-quarter of the observations on each side.
J
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K
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M
mean, arithmetic: The measure of central
location commonly called the average. It is calculated by adding together all
the individual values in a group of measurements and dividing by the number of
values in the group.
mean, geometric: The mean or average of a
set of data measured on a logarithmic scale.
measure of association: A quantified
relationship between exposure and disease; includes relative risk, rate ratio,
odds ratio.
measure of central location: A central
value that best represents a distribution of data. Measures of central location
include the mean, median, and mode. Also called the measure of central tendency.
measure of dispersion: A measure of the
spread of a distribution out from its central value. Measures of dispersion used
in epidemiology include the interquartile range, variance, and the standard
deviation.
median: The measure of central location
which divides a set of data into two equal parts.
medical surveillance: The monitoring of
potentially exposed individuals to detect early symptoms of disease.
midrange: The halfway point or midpoint
in a set of observations. For most types of data, it is calculated as the sum of
the smallest observation and the largest observation, divided by two. For age
data, one is added to the numerator. The midrange is usually calculated as an
intermediate step in determining other measures.
mode: A measure of central location, the
most frequently occurring value in a set of observations.
morbidity: Any departure, subjective or
objective, from a state of physiological or psychological well-being.
mortality rate: A measure of the
frequency of occurrence of death in a defined population during a specified
interval of time.
mortality rate, infant: A ratio
expressing the number of deaths among children under one year of age reported
during a given time period divided by the number of births reported during the
same time period. The infant mortality rate is usually expressed per 1,000 live
births.
mortality rate, neonatal: A ratio
expressing the number of deaths among children from birth up to but not
including 28 days of age divided by the number of live births reported during
the same time period. The neonatal mortality rate is usually expressed per 1,000
live births.
mortality rate, postneonatal: A ratio
expressing the number of deaths among children from 28 days up to but not
including 1 year of age during a given time period divided by the number of
lives births reported during the same time period. The postneonatal mortality
rate is usually expressed per 1,000 live births.
N
natural history of disease: The temporal
course of disease from onset (inception) to resolution.
necessary cause: A causal factor whose
presence is required for the occurrence of the effect (of disease).
nominal scale: Classification into
unordered qualitative categories; e.g., race, religion, and country of birth as
measurements of individual attributes are purely nominal scales, as there is no
inherent order to their categories.
normal curve: A bell-shaped curve that
results when a normal distribution is graphed.
normal distribution: The symmetrical
clustering of values around a central location. The properties of a normal
distribution include the following: (1) It is a continuous, symmetrical
distribution; both tails extend to infinity; (2) the arithmetic mean, mode, and
median are identical; and, (3) its shape is completely determined by the mean
and standard deviation.
numerator: The upper portion of a
fraction.
O
observational study: Epidemiological
study in situations where nature is allowed to take its course. Changes or
differences in one characteristic are studied in relation to changes or
differences in others, without the intervention of the investigator.
odds ratio: A measure of association
which quantifies the relationship between an exposure and health outcome from a
comparative study; also known as the cross-product ratio.
ordinal scale: Classification into
ordered qualitative categories; e.g., social class (I, II, III, etc.), where the
values have a distinct order, but their categories are qualitative in that there
is no natural (numerical) distance between their positive values.
outbreak: Synonymous with epidemic.
Sometimes the preferred word, as it may escape sensationalism associated with
the word epidemic. Alternatively, a localized as opposed to generalized
epidemic.
P
pandemic: An epidemic occurring over a
very wide area (several countries or continents) and usually affecting a large
proportion of the population.
percentile: The set of numbers from 0 to
100 that divide a distribution into 100 parts of equal area, or divide a set of
ranked data into 100 class intervals with each interval containing 1/100 of the
observations. A particular percentile, say the 5th percentile, is a cut point
with 5 percent of the observations below it and the remaining 95% of the
observations above it.
period prevalence: The amount a
particular disease present in a population over a period of time.
person-time rate: A measure of the
incidence rate of an event, e.g., a disease or death, in a population at risk
over an observed period to time, that directly incorporates time into the
denominator.
point prevalence: The amount of a
particular disease present in a population at a single point in time.
population: The total number of
inhabitants of a given area or country. In sampling, the population may refer to
the units from which the sample is drawn, not necessarily the total population
of people.
predictive value positive: A measure of
the predictive value of a reported case or epidemic; the proportion of cases
reported by a surveillance system or classified by a case definition which are
true cases.
prevalence: The number or proportion of
cases or events or conditions in a given population.
prevalence rate: The proportion of
persons in a population who have a particular disease or attribute at a
specified point in time or over a specified period of time.
proportion: A type of ratio in which the
numerator is included in the denominator. The ratio of a part to the whole,
expressed as a "decimal fraction'' (e.g., 0.2), as a fraction (1/5), or,
loosely, as a percentage (20%).
proportionate mortality: The proportion
of deaths in a specified population over a period of time attributable to
different causes. Each cause is expressed as a percentage of all deaths, and the
sum of the causes must add to 100%. These proportions are not mortality rates,
since the denominator is all deaths, not the population in which the deaths
occurred.
public health surveillance: The
systematic collection, analysis, interpretation, and dissemination of health
data on an ongoing basis, to gain knowledge of the pattern of disease occurrence
and potential in a community, in order to control and prevent disease in the
community.
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R
race-specific mortality rate: A mortality
rate limited to a specified racial group. Both numerator and denominator are
limited to the specified group.
random sample: A sample derived by
selecting individuals such that each individual has the same probability of
selection.
range: In statistics, the difference
between the largest and smallest values in a distribution. In common use, the
span of values from smallest to largest.
rate: An expression of the frequency with
which an event occurs in a defined population.
rate ratio: A comparison of two groups in
terms of incidence rates, person-time rates, or mortality rates.
ratio: The value obtained by dividing one
quantity by another.
relative risk: A comparison of the risk
of some health-related event such as disease or death in two groups.
representative sample: A sample whose
characteristics correspond to those of the original population or reference
population.
risk: The probability that an event will
occur, e.g. that an individual will become ill or die within a stated period of
time or age.
risk factor: An aspect of personal
behavior or lifestyle, an environmental exposure, or an inborn or inherited
characteristic that is associated with an increased occurrence of disease or
other health-related event or condition.
risk ratio: A comparison of the risk of
some health-related event such as disease or death in two groups.
S
sample: A selected subset of a
population. A sample may be random or non-random and it may be representative or
non-representative.
seasonality: Change in physiological
status or in disease occurrence that conforms to a regular seasonal pattern.
secondary attack rate: A measure of the
frequency of new cases of a disease among the contacts of known cases.
secular trend: Changes over a long period
of time, generally years or decades.
sensitivity: The ability of a system to
detect epidemics and other changes in disease occurrence. The proportion of
persons with disease who are correctly identified by a screening test or case
definition as having disease.
sentinel surveillance: A surveillance
system in which a pre-arranged sample of reporting sources agrees to report all
cases of one or more notifiable conditions.
sex-specific mortality rate: A mortality
rate among either males or females.
skewed: A distribution that is
asymmetrical.
specificity: The proportion of persons
without disease who are correctly identified by a screening test or case
definition as not having disease.
sporadic: A disease that occurs
infrequently and irregularly.
standard deviation: The most widely used
measure of dispersion of a frequency distribution, equal to the positive square
root of the variance.
standard error (of the mean): The
standard deviation of a theoretical distribution of sample means about the true
population mean.
sufficient cause: A causal factor or
collection of factors whose presence is always followed by the occurrence of the
effect (of disease).
survival curve: A curve that starts at
100% of the study population and shows the percentage of the population still
surviving at successive times for as long as information is available. May be
applied not only to survival as such, but also to the persistence of freedom
from a disease, or complication or some other endpoint.
T
table: A set of data arranged in rows and
columns.
table shell: A table that is complete
except for the data.
trend: A long-term movement or change in
frequency, usually upwards or downwards.
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V
validity: The degree to which a
measurement actually measures or detects what it is supposed to measure.
variable: Any characteristic or attribute
that can be measured.
variance: A measure of the dispersion
shown by a set of observations, defined by the sum of the squares of deviations
from the mean, divided by the number of degrees of freedom in the set of
observations.
vital statistics: Systematically
tabulated information about births, marriages, divorces, and deaths, based on
registration of these vital events.
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Y
years of potential life lost: A measure
of the impact of premature mortality on a population, calculated as the sum of
the differences between some predetermined minimum or desired life span and the
age of death for individuals who died earlier than that predetermined age.
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