Disease Detectives Terms

Sci-Oly Division B

sample

a selected subset of a population a sample can be random or nonrandom and representative or nonrepresentative.

sample, random

a sample of persons chosen in such a way that each one has the same (and known) probability of being selected.

sample, representative

a sample whose characteristics correspond to those of the original or reference population.

scale, interval

a measurement scale consisting of quantitative categories whose values are measured on a scale of equally spaced units, but without a true zero point (e.g., date of birth).

scale, nominal

a measurement scale consisting of qualitative categories whose values have no inherent statistical order or rank (e.g., categories of race/ethnicity, religion, or country of birth).

scale, ordinal

a measurement scale consisting of qualitative categories whose values have a distinct order but no numerical distance between their possible values (e.g., stage of cancer, I, II, III, or IV).

scale, ratio

a measurement scale consisting of quantitative categories whose values are intervals
with a true zero point (e.g., height in centimeters or duration of illness.)

scatter diagram (or scattergram)

a graphical display of the association between two variables in which a dot is plotted on the graph for each set of paired values for two continuous variables, with one variable plotted on the horizontal axis, and the other plotted on the vertical axis.

seasonality

change in physiologic status or in the occurrence of a disease, chronic condition, or type of injury that conforms to a regular seasonal pattern.

sensitivity

the ability of a test, case definition, or surveillance system to identify true cases; the proportion of people with a health condition (or the proportion of outbreaks) that are identified by a screening test or case definition (or surveillance system).

skewed

a distribution that is not symmetrical.

source (of infection)

the person, animal, object, or substance from which an infectious agent is transmitted to a host.

specificity

the ability or a test, case definition, or surveillance system to exclude persons without the health condition of interest; the proportion of persons without a health condition that are correctly identified as such by a screening test, case definition, or surveillance system.

spectrum of illness

the range of manifestations a disease process can take (e.g., from asymptomatic to mild clinical illness to severe illness and death).

sporadic

an event that occurs infrequently and irregularly.

spot map

a visual display of the geographic pattern of a health problem, in which a marker is placed on a map to indicate where each affected person lives, works, or might have been exposed.

standard deviation

a statistical summary of how dispersed the values of a variable are around its mean, calculated as the square root of the variance.

standard error (of the mean)

the standard deviation of a theoretical distribution of sample means of a variable around the true population mean of that variable. Standard error is computed as the standard deviation of the variable divided by the square root of the sample size.

statistical inference

generalizations developed from sample data, usually with calculated degrees of uncertainty.

statistical significance

the measure of how likely it is that a set of study results could have occurred by chance alone. Statistical significance is based on an estimate of the probability of the observed or a greater degree of association between independent and dependent variables occurring under the null hypothesis (see also P value).

study, analytic

a study, usually observational, in which groups are compared to identify and quantify associations, test hypotheses, and identify causes. Two common types are cohort studies and case-control studies.

study, case-control

an observational analytic study that enrolls one group of persons with a certain disease, chronic condition, or type of injury (case-patients) and a group of persons without the health problem (control subjects) and compares differences in exposures, behaviors, and other characteristics to identify and quantify associations, test hypotheses, and identify causes.

study, cohort

an observational analytic study in which enrollment is based on status of exposure to a certain factor or membership in a certain group. Populations are followed, and disease, death, or other health-related outcomes are documented and compared. Cohort studies can be either prospective or retrospective.

study, cross-sectional

a study in which a sample of persons from a population are enrolled and their exposures and health outcomes are measured simultaneously; a survey.

study, experimental

a study in which the investigator specifies the type of exposure for each person (clinical trial) or community (community trial) then follows the persons' or communities' health status to determine the effects of the exposure.

study, observational

a study in which the investigator observes rather than influences exposure and disease among participants. Case-control and cohort studies are observational studies (see also study, experimental).

study, prospective

an analytic study in which participants are enrolled before the health outcome of interest has occurred.

study, retrospective

an analytic study in which participants are enrolled after the health outcome of interest has occurred. Case-control studies are inherently retrospective.

subclinical

without apparent symptoms.

surveillance, active

public health surveillance in which the health agency solicits reports.

surveillance, medical

monitoring of a person who might have been exposed to an infectious, chemical, radiologic, or other potentially causal agent, for the purpose of detecting early symptoms.

surveillance, passive

public health surveillance in which data are sent to the health agency without prompting.

surveillance, sentinel

a surveillance system that uses a prearranged sample of sources (e.g., physicians, hospitals, or clinics) who have agreed to report all cases of one or more notifiable diseases.

surveillance, syndromic

(1) the monitoring of the frequency of illnesses with a specified set of clinical features among a given population without regard to the specific diagnoses, if any, that are assigned to them by clinicians. (2) A system for early detection of outbreaks whereby health department staff, assisted by automated acquisition of data routinely collected for other purposes and computer generation of statistical signals, monitor disease indicators, particularly those associated with possible terrorism-related biologic and chemical agents, continually or at least daily to detect outbreaks earlier than would otherwise be possible with traditional public health methods.
survey a systematic canvassing of persons to collect information, often from a representative sample of the population.
survival curve a line graph that begins with 100% of the study population and displays the percentage of the population still surviving at successive points in time. A survival curve can also be used to depict freedom from a health problem, complication, or another endpoint.

symmetrical

a type of distribution where the shapes to the right and left of the central location are the same. Normal, bell-shaped distributions are symmetrical; the mean, median, and mode are the same.

symptom

any indication of disease noticed or felt by a patient.

syndrome

a combination of symptoms characteristic of a disease or health condition; sometimes refers to a health condition without a clear cause (e.g., chronic fatigue syndrome).

quarantine

the separation of well persons who have been exposed or are suspected to have been exposed to a communicable disease, to monitor for illness and to prevent potential transmission of infection to susceptible persons during the incubation period. Quarantine refers to separation of potentially exposed but well persons; isolation refers to separation of ill persons.

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 relative frequency with which an event occurs among a defined population per unit of time, calculated as the number of new cases or deaths during a specified period divided by either person-time or the average (midinterval) population. In epidemiology, it is often used more casually to refer to proportions that are not truly rates (e.g., attack rate or case-fatality rate).

rate ratio

a measure of association that quantifies the relation between an exposure and a health outcome from an epidemiologic study, calculated as the ratio of incidence rates or mortality rates of two groups

ratio

the relative size of two quantities, calculated by dividing one quantity by the other.

record

in a line listing, each row is a record or observation. A record represents data related to a single case.

relative risk

a general term for measures of association calculated from the data in a two-by-two table, including risk ratio, rate ratio, and odds ratio (see also risk ratio).

reservoir

the habitat in which an infectious agent normally lives, grows, and multiplies, which can include humans, animals, or the environment.

risk

the probability that an event will occur (e.g., that a person will be affected by, or die from, an illness, injury, or other health condition within a specified time or age span).

risk factor

an aspect of personal behavior or lifestyle, an environmental exposure, or a hereditary characteristic that is associated with an increase in the occurrence of a particular disease, injury, or other health condition.

risk ratio

a measure of association that quantifies the association between an exposure and a health outcome from an epidemiologic study, calculated as the ratio of incidence proportions of two groups.

odds ratio

a measure of association used in comparative studies, particularly case-control studies, that quantifies the association between an exposure and a health outcome; also called the cross-product ratio.

outbreak

the occurrence of more cases of disease, injury, or other health condition than expected in a given area or among a specific group of persons during a specific period. Usually, the cases are presumed to have a common cause or to be related to one another in some way. Sometimes distinguished from an epidemic as more localized, or the term less likely to evoke public panic (see also epidemic).

outbreak, common-source

an outbreak that results from persons being exposed to the same harmful influence (e.g., an infectious agent or toxin). The exposure period can be brief or can extend over days, weeks, or longer, with the exposure being either intermittent or continuous.

outbreak, point-source

a common source outbreak in which the exposure period is relatively brief so that all cases occur within one incubation period.

outbreak, propagated

an outbreak that spreads from person to person rather than from a common source.

outcome(s)

any or all of the possible results that can stem from exposure to a causal factor or from preventive or therapeutic interventions; all identified changes in health status that result from the handling of a health problem.

outlier

a value substantively or statistically different from all (or approximately all) of the other values in a distribution.

P value

the probability of observing an association between two variables or a difference between two or more groups as large or larger than that observed, if the null hypothesis were true. Used in statistical testing to evaluate the plausibility of the null hypothesis (i.e., whether the observed association or difference plausibly might have occurred by chance).

pandemic

an epidemic occurring over a widespread area (multiple countries or continents) and usually affecting a substantial proportion of the population.

pathogenicity

the ability of an agent to cause disease after infection, measured as the proportion
of persons infected by an agent who then experience clinical disease.

percentile

a set of cut points used to divide a distribution or a set of ranked data into 100 parts of equal area with each interval between the points containing 1/100 or 1% of the observations. For example, the 5th percentile is a cut point with 5% of the observations below it and the remaining 95% above it.

person-time rate

the incidence rate calculated as the number of new cases among a population divided by the cumulative person-time of that population, usually expressed as the number of events per persons per unit of time.

person-time

the amount of time each participant in a cohort study is observed and disease-free, often summed to provide the denominator for a person-time rate.

phylogenetic tree

a branching chart that indicates the evolutionary lineage or genetic relatedness of organisms.

pie chart

a circular graph of a frequency distribution in which each segment of the pie is proportional in size to the frequency of corresponding category.

population

the total number of inhabitants of a geographic area or the total number of persons in a particular group (e.g., the number of persons engaged in a certain occupation).

population pyramid

a graphical display of the age-sex distribution of a population, constructed with a horizontal histogram of the age distribution of males pointing to the left, and the corresponding horizontal histogram of age distribution of females pointing to the right.

portal of entry

a pathway into the host that gives an agent access to tissue that will allow it to multiply or act.

portal of exit

a pathway by which an agent can leave its host.

predictive value positive

the proportion of cases identified by a test, reported by a surveillance system, or classified by a case definition that are true cases, calculated as the number of true-positives divided by the number of true-positives plus false-positives.

prevalence

the number or proportion of cases or events or attributes among a given population.

prevalence rate

the proportion of a population that has a particular disease, injury, other health condition, or attribute at a specified point in time (point prevalence) or during a specified period (period prevalence).

prevalence, period

the amount of a particular disease, chronic condition, or type of injury present among a population at any time during a particular period.

prevalence, point

the amount of a particular disease, chronic condition, or type of injury present among a population at a single point in time.

privacy rule

a set of regulations based on the Health Insurance Portability and Accountability Act to protect the privacy of individually identifiable health information.

proportion

a 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), a fraction (1/5), or a percentage (20%).

proportion, attributable

a measure of the impact of a causative factor on the public health; the proportion of a health state or event among exposed persons that can be attributed to the exposure also called attributable risk percent.

proportionate mortality

the proportion of deaths among a population attributable to a particular cause during a selected period. Each cause of death is expressed as a percentage of all deaths, and the sum of the proportionate mortality for all causes must equal 100%. These proportions are not mortality rates because, in proportionate mortality, the denominator is all deaths instead of the population among whom the deaths occurred.

map, area (shaded, choropleth)

a visual display of the geographic pattern of a health problem, in which a marker is placed on a map to indicate where each affected person lives, works, or might have been exposed.

mean (or average)

commonly called the average; it is the most common measure of central tendency.

mean, arithmetic

the measure of central location, commonly called the average, calculated by adding all the 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 a particular health problem (e.g., risk ratio, rate ratio, and odds ratio.)

measure of central location

a central value that best represents a distribution of data. Common measures of central location are the mean, median, and mode also called the measure of central tendency.

measure of spread

a measure of the distribution of observations out from its central value. Measures of spread used in epidemiology include the interquartile range, variance, and the standard deviation.

measurement scale

the complete range of possible values for a measurement.

median

the measure of central location that divides a set of data into two equal parts, above and below which lie an equal number of values (see also measure of central location).

midrange

the halfway point, or midpoint, in a set of observations. For the majority of data, the midrange is calculated by adding the smallest observation and the largest observation and dividing by two. The midrange is usually calculated as an intermediate step in determining other measures.

mode

the most frequently occurring value in a set of observations (see also measure of central location).

mode of transmission

the manner in which an agent is transmitted from its reservoir to a susceptible host (see also transmission).

morbidity

disease; any departure, subjective or objective, from a state of physiological or psychological health and well-being.

mortality

death.

mortality rate

a measure of the frequency of occurrence of death among a defined population during a specified time interval.

mortality rate, age-adjusted

a mortality rate that has been statistically modified to eliminate the effect of different age distributions among different populations.

mortality rate, age-specific

a mortality rate limited to a particular age group, calculated as the number of deaths among the age group divided by the number of persons in that age group, usually expressed per 100,000.

mortality rate, cause-specific

the mortality rate from a specified cause, calculated as the number of deaths attributed to a specific cause during a specified time interval among a population divided by the size of the midinterval population.

mortality rate, crude

a mortality rate from all causes of death for an entire population, without adjustment.

mortality rate, infant

the mortality rate for children aged

mortality rate, neonatal

the mortality rate for children from age birth up to, but not including, 28 days. In calculating neonatal mortality rates, the numerator is the number of deaths among this age group during a given period, and the denominator is the number of live births reported during the same period. The neonatal mortality rate is usually expressed per 1,000 live births.

mortality rate, postneonatal

the mortality rate for children from age 28 days up to, but not including, 1 year. In calculating postneonatal mortality rates, the numerator is the number of deaths among this age group during a given period, and the denominator is the number of live births during the same period.. The postneonatal mortality rate is usually expressed per 1,000 live births.

mortality rate, race/ethnic-specific

a mortality rate limited to a specified racial or ethnic group both numerator and denominator are limited to that group.

mortality rate, sex-specific

a mortality rate among either males or females.