a factor (e.g., a microorganism or chemical substance) or form of energy whose presence, excessive presence, or in the case of deficiency diseases, relative absence is essential for the occurrence of a disease or other adverse health outcome.
any of a variety of proteins in the blood that are produced in response to an antigen as an immune response.
any substance (e.g., a toxin or the surface of a microorganism or transplanted organ) recognized as foreign by the human body and that stimulates the production of antibodies.
any of a group of viruses that are transmitted between hosts by mosquitoes, ticks, and other arthropods.
an organism that has jointed appendages and segmented external skeleton (e.g., flies, mosquitoes, ticks, or mites).
the statistical relation between two or more events, characteristics, or other variables.
a type of distribution where the shape to the right and left of the central location is not the same. Often referred to as a skewed distribution; the mean, median, and mode of an asymmetrical distribution are not the same.
a form of incidence that measures the proportion of persons in a population who experience an acute health event during a limited period (e.g., during an outbreak), calculated as the number of new cases of a health problem during an outbreak divided by the size of the
population at the beginning of the period, usually expressed as a percentage or per 1,000 or 100,000 population (see also incidence proportion).
attack rate, secondary
a measure of the frequency of new cases of a disease among the contacts of known patients.
a risk factor that is an intrinsic characteristic of the individual person, animal, plant, or other type of organism under study (e.g., genetic susceptibility, age, sex, breed, weight).
one of the dimensions of a graph in a rectangular graph, the x-axis is the horizontal axis, and the y-axis is the vertical axis.
a visual display in which each category of a variable is represented by a bar or column bar charts are used to illustrate variations in size among categories.
bar chart, 100% component
a stacked bar chart in which all bars or columns are the same length, and the measured axis represents 0%-100%.
bar chart, deviation
a bar chart displaying either positive or negative differences from a baseline.
bar chart, grouped
a bar chart displaying quantities of two variables, represented by adjoining bars or columns (i.e., a group) of categories of one variable, separated by space between groups.
bar chart, stacked
a bar chart displaying quantities of two variables, represented by subdivided bars or columns (the subdivisions representing the categories of one variable) separated by space between bars or columns.
a systematic deviation of results or inferences from the truth or processes leading to such systematic deviation; any systematic tendency in the collection, analysis, interpretation, publication, or review of data that can lead to conclusions that are systematically different from the truth. In epidemiology, does not imply intentional deviation.
systematic difference in the collection of data regarding the participants in a study (e.g., about exposures in a case-control study, or about health outcomes in a cohort study) that leads to an incorrect result (e.g., risk ratio or odds ratio) or inference.
systematic difference in the enrollment of participants in a study that leads to an incorrect result (e.g., risk ratio or odds ratio) or inference.
having two data peaks.
birth rate, crude
the number of live births during a specified period divided by the mid-period population, usually expressed per 1,000 population.
a visual display that summarizes data by using a "box and whiskers" format to indicate the minimum and maximum values (ends of the whiskers), interquartile range (length of the box), and median (line through the box).
a person or animal that harbors the infectious agent for a disease and can transmit it to others, but does not demonstrate signs of the disease. A carrier can be asymptomatic (never indicate signs of the disease) or can display signs of the disease only during the incubation period, convalescence, or postconvalescence. The period of being a carrier can be short (a transient carrier) or long (a chronic carrier).
an instance of a particular disease, injury, or other health conditions that meets selected criteria (see also case definition). Using the term to describe the person rather than the health condition is discouraged.
a set of uniformly applied criteria for determining whether a person should be identified as having a particular disease, injury, or other health condition. In epidemiology, particularly for an outbreak investigation, a case definition specifies clinical criteria and details of time, place, and person.
case-fatality rate (also called case-fatality ratio)
the proportion of persons with a particular
condition (e.g., patients) who die from that condition. The denominator is the number of persons with the condition; the numerator is the number of cause-specific deaths among those persons.
the first case or instance of a patient coming to the attention of health authorities.
in a case-control study, a person who has the disease, injury, or other health condition that meets the case definition.
the case or instance of a patient responsible for transmitting infection to others; the instance of a patient who gives rise to an outbreak or epidemic.
a factor that contributes to a sufficient cause (see cause, sufficient).
cause of disease
a factor (e.g., characteristic, behavior, or event) that directly influences the occurrence of a disease. Reducing such a factor among a population should reduce occurrence of the disease.
a factor that must be present for a disease or other health problem to occur.
a factor or collection of factors whose presence is always followed by the occurrence of a particular health problem.
the enumeration of an entire population, usually including details on residence, age, sex, occupation, racial/ethnic group, marital status, birth history, and relationship to the head of household.
central location (also called central tendency)
a statistical measurement to quantify the middle
or the center of a distribution. Of the multiple ways to efine central tendency, the most common are the mean, median, and mode.
chain of infection
the progression of an infectious agent that leaves its reservoir or host through a portal of exit, is conveyed by a mode of transmission, and then enters through an appropriate portal of entry to infect a susceptible host.
unnecessary or confusing visual elements in charts, illustrations, or graphs. The term was first used by Edward Tufte in his book, The Visual Display of Quantitative Information (1983).
the span of values of a continuous variable that are grouped into a single category, usually to create a frequency distribution for that variable.
the values at the upper and lower ends of a class interval.
the medical features (e.g., symptoms, medical examination findings, and laboratory results) that are used in a case definition.
a disease that has been manifested by its symptoms and features.
an aggregation of cases of a disease, injury, or other health condition (particularly cancer and birth defects) in a circumscribed area during a particular period without regard to whether the number of cases is more than expected (often the expected number is not known).
a well-defined group of persons who have had a common experience or exposure and are then followed up, as in a cohort study or prospective study, to determine the incidence of new diseases or health events.
a group of persons born during a particular period or year.
a group in an analytic study (e.g., a cohort or case-control study) with whom the primary group of interest (exposed group in a cohort study or case-patients in a case-control study) is compared. The comparison group provides an estimate of the background or expected incidence of disease (in a cohort study) or exposure (in a case-control study).
a range of values for a measure (e.g., rate or odds ratio) constructed so that the range has a specified probability (often, but not necessarily, 95%) of including the true value of the measure.
the end points (i.e., the minimum and maximum values) of a confidence.
the distortion of the association between an exposure and a health outcome by a third variable that is related to both.
exposure to a source of an infection; a person who has been exposed.
exposure or transmission of an agent from a source to a susceptible host through touching (e.g., from a human host by kissing, sexual intercourse, or skin-to-skin contact) or from touching an infected animal or contaminated soil or vegetation.
capable of being transmitted from one person to another by contact or close proximity.
a two-variable table of cross-tabulated data.
in a case-control study, a member of the group of persons without the health problem under study.
when referring to a rate, an overall or summary rate for a population, without adjustment.
in a frequency distribution, the number or proportion of observations with a particular value and any smaller value.
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 and quartiles and other percentiles.