Pubic Health Terms Flashcards
What is accuracy
Accuracy is the extent to which a measurement reflects the true value
What is precision
Precise” means sharply defined or measured. Data can be very precise, but inaccurate.
- has very little scatter and repeat measurements will give more or less the same value
What can cause high precision but poor accuracy
- a systematic bias has been introduced - using an instrument where the zero position has not been set properly
Why do you use age-specific rates
The application of age-specific rates in a population of interest to a standardized age distribution in order to eliminate differences in observed rates that result from age differences in population composition
What is an 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.
What is an age specific rate
- A rate limited to a particular age group
- The numerator is the number of occurrences in that age group; the denominator is the number of persons in that age group in the population.
What is airborne transmission
Airborne transmission refers to situations where droplet nuclei (residue from evaporated droplets) or dust particles containing microorganisms can remain suspended in air for long periods of time
List diseases that are capable of airborne transmission
- Influenza
- Whooping cough
- Pneumonia
- Tuberculosis
- Polio
What is analysis of variance (ANOVA)
- A collection of statistical models and their associated estimation procedures used to analyse the differences among group means in a sample
What is association
Statistical relationship between two or more events, characteristics, or other variables
What is 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
How is attributable proportion calculated
Pe(RR-1) / 1+Pe(RR-1)
What is a bar chart
A graphical technique for presenting discrete data organized sothat each observation can fall into one and only one category of the variable. - Frequencies are listed along one axis and categories of the variable are listed along the other axis.
- The lengths of the bars represent frequencies of each group of observations.
What is 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
Give exampels of types of bias
- Selection bias
- detection bias
- information bias
- misclassification
- recall bias
What is a box plot
A visual display that summarizes data using a ‘box and whiskers’ format to show the minimum and maximum values (ends of the whiskers), interquartile range (length of the box), and median (line through the box)
What is a carrier
A person or animal without apparent disease that harbors a specific infectious agent and is capable of transmitting the agent to others
What is a case
In epidemiology, a countable instance in the population or study group of a particular disease, health disorder, or condition under investigation
What is a case control study
A type of observational 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
what is 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.
What is a case report study
A type of descriptive study that consists of a careful, detailed profile of an individual patient.
What is a case series study
A type of descriptive study that describes characteristics of number of patients with a given disease
What is causality
The relating of causes to the effects they produce. Some of the criteria for inferring a causal relationship between an implicated food and illness include: strength of association, consistency of the observed association, temporal sequence of events biological plausibility of the observed association, effect of removing the exposure, dose-response relationships, and the exclusion of alternate explanations (Bradford-Hill criteria).
What measures causality
- Bradford hill criteria
What is the casue of the disease
A factor that is associated with the incidence of the disease so that if the intensity or prevalence of the factor in a population changes, the incidence of the disease changes in ways that cannot be explained by changes in other factors.
What is a 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.
What is the chi square test
A test of statistical significance. A Chi Square (X2) test looks at the difference between what we observe in the data and what we would expect if the exposure was not associated with the illness.
What is a clinical trial
A clinical trial is an experiment in which a treatment is administered to humans in order to evaluate its efficacy and safety.
What is a cluster trial
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.
- cluster randomised trial is when rather than individuals being randomized to treatment groups, pre-existing groups are randomized to treatment groups (e.g. schools, villages)
What is a 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. For example, a group of people born during a particular period or year is called a birth cohort.
What is a cohort study
- A type of observational study that is usually prospective.
- 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 between groups eg those that are exposed to some factor and those that are not.
What is a common source outbreak
An outbreak that results from a group of persons being exposed to a common noxious influence, such as an infectious agent or toxin. If the group is exposed over a relatively brief period of time, so that all cases occur within one incubation period, then the common source outbreak is further classified as a point source outbreak.
What is a communiable disease
An infectious disease transmitted from an infected person, animal, or reservoir to a susceptible host through an intermediate plant, animal, or the inanimate environment.
What is a 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 end points of the confidence interval are called the confidence limits. Usually the 95% confidence interval is reported.
What is a confounding variable
This can occur when an association between a risk factor and disease can be explained by a factor associated with both disease and risk factor.
What is a contingency table
A two-variable table with cross-tabulated data used to calculate a potential association. This is also called a 2X2 table; odds ratios or relative risks are typically calculated from a contingency table:
What is a control
In a case-control study, comparison group of persons without disease.
What is a crossover trial
A randomized trial in which participants are randomized to treatment sequence rather than to one of two or more treatments (as in a parallel group randomized controlled trial). All trial participants receive all treatments, and the response to treatments at the end of each period are compared. Crossover trials are useful for subjective measurements such as pain, or when the effect of treatment is reversible
What is a crude mortality rate
The mortality rate from all causes of death for a population.
What is a 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.
what is a 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.
What is a cumulative incidence
A measure of the risk or probability of acquiring disease. The number of new cases of diseases in a specified time period divided by the number of individuals at the beginning of the observation period. Technically, cumulative incidence is not a rate, but a proportion
What is a cross-sectional study
A measure of the risk or probability of acquiring disease. The number of new cases of diseases in a specified time period divided by the number of individuals at the beginning of the observation period. Technically, cumulative incidence is not a rate, but a proportion
What is death to case ratio
The number of deaths attributed to a particular disease
during a specified time period divided by the number of new cases of that disease identified during that same time period
What is demographic information
The ‘person’ characteristics–age, sex, race, and occupation–of descriptive epidemiology used to characterize the populations at risk.
define 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).
define descriptive epidemiology
The aspect of epidemiology concerned with organizing and summarizing health-related data according to time, place, and person.
define detection bias
This type of bias can occur when persons with a risk factor are more likely to have disease detected because of more intense follow-up
define determinant
Any factor, whether event, characteristic, or other definable entity,
that brings about change in a health condition, or in other defined characteristics.
Define direct transmission
The immediate transfer of an agent from a reservoir to a susceptible host by direct contact or droplet spread.
Describe 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.
Describe a dot plot
A visual display of the actual data points of a continuous variable.
Describe droplet spread
The direct transmission of an infectious agent from a reservoir to a susceptible host by spray with relatively large, short-ranged aerosols produced by sneezing, coughing, or talking.
describe an ecological study
A type of study involving the comparison of disease frequency (incidence or prevalence) between populations that are different with respect to one or more risk factors of interest. The risk factor information is not known for individual subjects, but rather as a population characteristic. For example pollution exposure may not be known on an individual level, but is known at a local area district level.
describe effect modification
This refers to variation in the magnitude of a measure of exposure effect across levels of another variable.
describe endemic disease
The constant presence of a disease or infectious agent within a given geographic area or population group
Describe environmental factor
An extrinsic factor (geology, climate, insects, sanitation, health services, etc.) that affects the agent and the opportunity for exposure.
Describe 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.
Describe the epidemic curve
A histogram that shows the course of a disease outbreak or epidemic by plotting the number of cases by time of onset.
Describe the epidemic peroid
A time period when the number of cases of disease reported is greater than expected.
Describe the epidemiological 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
Describe epidemiology
The study of the incidence, distribution and determinants of diseases in humans, with a view to identifying what causes a particular disease and by doing so discovering ways of preventing the disease
define 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.
define excess deaths
How many more deaths have occurred than we would expect, based on historical trends.
define fecal-oral transmission
A type of indirect transmission. Fecal-oral transmission is usually associated with organisms that infect the digestive system. Microorganisms enter the body through ingestion of contaminated food and water.
define frequency distribution
A complete summary of the frequencies of the values or categories of a variable; often displayed in either a histogram, a smoothed distribution curve (assuming an underlying distribution such as a normal [Gaussian] distribution, or a two column table: the left column lists the individual values or categories, the right column indicates the number of observations in each category.
define gravidity
Gravidity is defined as the total number of times a woman has been pregnant. This is distinguished from parity, which is defined as the total number of live births ever had by the woman.
define hazard ratio
The risk of an event (death/disease) at any time point in one group compared to the other. Similar interpretation to a relative risk.
define health
A state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity.
Define health indicator
A measure that reflects, or indicates, the state of health of persons in a defined population, e.g., the infant mortality rate.
Define 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.
Define histogram
A graphic representation of the frequency distribution of a continuous variable. Rectangles are drawn in such a way that their bases lie on a linear scale representing different intervals, and their heights are proportional to the frequencies of the values within each of the intervals.
Define host
A person or other living organism that can be infected by an infectious agent under natural conditions.
Define host factor
An intrinsic factor (age, race, sex, behaviors, etc.) that influences an individual’s exposure, susceptibility, or response to a causative agent.
Define hyperendemic disease
A disease that is constantly present at a high incidence and/or prevalence rate.
Define hypothesis
An idea or explanation for something that is based on known or assumed facts that have yet to be proved.
define null hypothesis
- the first step in testing for statistical significant in whcih it is assumed that there is no differnece between two or more measured phenomena or that two samples derive come from the same general population
- A null hypothesis is rejected if the observed data is significantly unlikely to have occured if the null hypothesis were true
Define alternative hypothesis
- The hypothesis to be adopted if the null hypothesis proves implausible in which for example, exposure is associated with disease
Define immune
Refers to someone who shows no clinical signs of infection after exposure
to a pathogen.
define active immunity
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.
define herd immunity
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
define passive immunity
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).
define 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. Usually reported as a number per 10,000 (or 100,000) person- years
Define incubation peroid
A period of subclinical or unapparent pathologic changes following exposure, ending with the onset of symptoms of infectious disease.
define 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).
Define index case
The first case to come to the attention of a disease investigator.
Define indirect transmission
The transmission of an agent carried from a reservoir to a susceptible host by suspended air particles or by animate (vector) or inanimate (vehicle) intermediaries. Indirect contact transmission refers to situations where a susceptible person is infected from contact with a contaminated surface.
Define information bias
The type of bias can occur when interviewers who are aware of the identity of subjects or factors of interest (e.g., case or control) and collect information unevenly between subjects
Define interaction
- Tow or more component causes acting in the same sufficient cause
- an interaction may arise when considering the relationship among three or more variables and describes a situation in which the effect of one causal varaible on the outcome depends on the state of a second causal variable
Define international classification of disease
The ICD provides the ground rules for coding and classifying cause-of-death data. The ICD is developed collaboratively between the World Health Organization (WHO) and ten international centers. The purpose of the ICD is to promote international comparability in the collection, classification, processing, and presentation of health statistics.
Define interquartile range
The central portion of a distribution, calculated as the difference between the third quartile (75th centile) and the first quartile (25th centile); this range includes one-half of the observations in the set, leaving one- quarter of the observations on each side.
define latency peroid
A period of subclinical or unapparent pathologic changes
following exposure, ending with the onset of symptoms of chronic disease
Define life expectancy
Life expectancy is the average number of years of life remaining to a person at a particular age and is based on a given set of age-specific death rates, generally the mortality conditions existing in the period mentioned. Life expectancy may be determined by race, sex, or other characteristics using age- specific death rates for the population with that characteristic.
define logarithmic scale
A proportional scale such that the distance between 1 and 2 is the same as the distance between 2 and 4, and the distance between 4 and 8 etc.
What is the arithmetic mean
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.
What is the geometric mean
The mean or average of a set of data measured on a logarithmic (multiplicative) scale; an example of a logarithmic scale is when data are transformed to a scale such that the distances between 1, 10, 100, 1000, 10,000 etc. is the same
What is the measure of association
A quantified relationship between exposure and disease; includes relative risk, rate ratio, odds ratio etc.
What is the 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
define 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.
define median
The measure of central location that divides a set of data into two equal parts. The median is found two different ways depending on the number of observations. If the number of observations is odd, then there is a unique central point. For samples with an even number of observations, there is no unique central point, and the two middle points would be averaged to obtain the median.
define medical surveillance
The monitoring of potentially exposed individuals to detect early symptoms of disease.
define misclassification
This type of bias can occur when there is error in classifying subjects by disease or risk factor that tends to distort associations between disease and risk factors
define mode
A measure of central location, the most frequently occurring value in a set of observations.
define morbidity
Any departure, subjective or objective, from a state of physiological or psychological well-being.
define mortality rate
A measure of the frequency of occurrence of death in a defined population during a specified interval of time.
Define natural history of disease
The temporal course of disease from onset (inception) to resolution. Many diseases have certain well-defined stages that, taken together, are referred to as the “natural history of the disease.” These stages are as follows: 1. Stage of pathological onset, 2. Pre-symptomatic stage: from the onset to the first appearance of symptoms and/or signs, and 3. Clinical manifestation of disease, which may progress to fatal termination, be subject to remission or relapses, or regress spontaneously, leading to recovery.
Define necessary cause
A causal factor whose presence is required for the occurrence of the effect (of disease)
Define negative predictive value
The probability that people with a negative screening test result truly do not have the disease the screening test intends to identify.
Define 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.
Define normal curve
Also known as Gaussian curve. A bell-shaped curve that results when a normal distribution is graphed.
Define normal distribution
Also known as Gaussian 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. Also known as the Gaussian distribution.
Define number needed to treat
The number of patients that need to be treated to have an impact on one person, calculated as 100 divided by the (absolute) risk difference between two groups.
Define 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.
Define odds ratio
A measure of association that quantifies the relationship between an exposure and health outcome from a comparative study; it is the odds of being exposed among cases divided by the odds of being exposed among controls
Define 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.
Define 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.
Define pandemic
An epidemic occurring over a very wide area (several countries or continents) and usually affecting a large proportion of the population. COVID-19 and the 1918 Spanish Influenza are examples of pandemics.
Define parallel group randomised controlled trial
A randomized trial in which participants are randomized to one of two or more treatments. After follow-up is complete the response to treatments are compared between randomization groups.
Define partiy
Parity is defined as the total number of live births ever had by the woman
Define pathogenicity
The proportion of persons infected, after exposure to a causative agent, who then develop clinical disease.
define 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.
define peroid prevalence
The amount a particular disease present in a population over a period of time.
define 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
define pie chart
A circular chart in which the size of each ‘slice’ is proportional to the frequency of each category of a variable
define point prevalence
The amount of a particular disease present in a population at a single point in time.
Define 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.
Define positive predictive value
The probability that people with a positive
screening test result truly have the disease the screening test intends to identify
Define prevalence
The number or proportion of cases or events or conditions in a given population.
define 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. Prevalence rates do not differentiate between old and new cases of disease. It is a function of the incidence rate and the mean duration of illness.
define 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%).
define prospective study
At the time a study begins, either the exposure or the outcome of interest has not yet occurred.
define 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.
define P value
A measure of how likely the observed results, or a result more extreme would occur when there is no real association (i.e. how likely the observed results would occur by chance alone). Statistical significance is usually shown when p<0.05
define questionnaire
A set of questions used to collect information. Typically questions can be grouped into the following categories: identifying, demographic, clinical, risk, and reported information.
define random sample
A sample derived by selecting individuals such that each individual has the same probability of selection.
define 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. If a percentage range is specified, such as the 95% range this is where 95% of the values lie, between the 2.5th and 97.5th percentiles
define rate
An expression of the frequency with which an event occurs in a defined population.
define rate ratio
A comparison of two groups in terms of incidence rates, person-time rates, or mortality rates.
define ratio
The value obtained by dividing one quantity by another.
define recall bias
This type of bias can occur in retrospective studies when persons with disease tend to report past exposures and events differently from persons without disease.
Define regression
A statistical method used to determine the strength and character
of the relationship between one dependent variable (usually denoted by Y) and a
series of other variables (known as independent variables).
Define relative risk
Also known as risk ratio. A comparison of the risk of some health-related event such as disease or death in two groups, for example the event could be death and the groups could be smokers (exposed) and non- smokers (unexposed)
define reliability
Refers to the consistency of a measurement when repeated on the same subjects.
Define representative sample
A sample whose characteristics correspond to those of the original population or reference population.
Define reproductive rate
A metric used to describe the contagiousness or transmissibility of infectious agents, which is usually estimated with complex mathematical models developed using various sets of assumptions. It is an estimate of the average number of new cases of a disease that each case generates, at a given point in time.
define reservoir
The habitat in which an infectious agent normally lives, grows and multiplies; reservoirs can be human, animal, and environmental.
define retrospective study
At the time a study begins, both the exposure and the outcome of interest has occurred.
define 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. Usually expressed as 1 in x, e.g. 1 in 100 (1%)
define risk difference
The absolute difference in risk between two groups
define 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.
define sample
A selected subset of a population. A sample may be random or non- random and it may be representative or non-representative.
define scatter plot
A graph in which each dot represents paired values for two continuous variables, with the x-axis (horizontal axis) representing one variable and the y-axis (vertical axis) representing the other; used to display the relationship between the two variables; also called a scattergram.
define selection bias
This type of bias can occur when there are differential selection rates of subjects by disease and/or risk factor characteristics.
Define sensitivity
The proportion of persons with disease who are correctly identified by a screening test or case definition as having disease. Usually expressed as a percentage. Also often known as the Detection Rate (especially in the field of antenatal screening).
Define significance test
A test of statistical significance shows how likely one is to get a measure of association as strong as the observed one if there is no difference between the groups.
Define skewed
A distribution that is asymmetrical. Sometimes a transformation of the data for example by taking the logarithm or square root can make the distribution symmetrical. Blood biomarkers are often log-transformed to make them symmetrical
define specificity
he proportion of persons without disease who are correctly identified by a screening test or case definition as not having disease. Usually expressed as a percentage. Often the false-positive rate is reported instead (especially in the field of antenatal screening), which is the complement of specificity (e.g. if specificity is 95% the false-positive rate is 5%).
define sporadic
A disease that occurs infrequently and irregularly
define standard deviation
The most widely used measure of dispersion of
a frequency distribution, equal to the square root of the variance.
Define standard error of the mean
The standard deviation of a theoretical distribution of sample means about the true population mean. Used in calculating confidence intervals.
Define sufficient cause
A causal factor or collection of factors whose presence is always followed by the occurrence of the effect (of disease).
Define 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. The visual representation of the curve is usually called the Kaplan-Meier curve
Define T test
A t-test is a type of inferential statistic used to determine if there is a
significant difference between means; it could be the means between two
independent groups (unpaired t-test) or it could be the difference ‘before’ and ‘after’
e.g. an intervention (paired t-test), or it could be testing whether the mean in a
group is different from a specified mean (one-sample t-test). The test assumes data
follow a normal (Gaussian) distribution. If the data do not a non-parametric test
such as the Wilcoxon rank sum test aka Mann Whitney U-test (for unpaired data) or
Wilcoxon signed rank test (for paired data) can be used.
define transmission of infection
Any mode or mechanism by which an infectious agent is spread through the environment or to another person. There are two types of transmission: direct and indirect.
Define trend
A long-term movement or change in frequency, usually upwards or downwards.
Define type I error
In statistical significance testing a Type I error occurs when the null hypothesis is rejected when it is true i.e. a false-positive result
Define type II error
In statistical significance testing a Type 2 error occurs when there is non-rejection of a false null hypothesis i.e. a false-negative result
define validity
The degree to which a measurement actually measures or detects what it is supposed to measure.
define variable
Any characteristic or attribute that can be measured.
define variance
A measure of the dispersion (spread) shown by a set of observations, defined by the sum of the squares of deviations from the mean, divided by the sample size minus 1.
Define vector
An animate intermediary in the indirect transmission of an agent that carries the agent from a reservoir to a susceptible host.
define vector borne transmission
Vectors are animals that are capable of transmitting diseases. Examples of vectors are flies, mites, fleas, ticks, rats, and dogs
define vehicle
An inanimate intermediary in the indirect transmission of an agent that carries the agent from a reservoir to a susceptible host.
define Z score
A transformation used where individual values of a continuous variable have the mean subtracted and are divided by the standard deviation.
