Definitions Flashcards
Epidemiology
The study of the frequency, distribution, and determinants of health and disease in populations, and the application of this study to the control of diseases.
Health
A state of complete physical, mental and social well-being, and not merely the absence of disease or infirmity.
Disease
A physiological/psychological dysfunction.
Epidemiologist
One who understands the principles of epidemiologic research and has the experience to apply them. It is not necessary to be a physican, veterinarian or statistician.
Illness
A subjective state of the person who feels aware of not being well.
Disease sign
Something you can see or measure i.e. fever
Disease symptom
Self-reported, cannot see or measure i.e. aches
Disease syndrome
A combination of signs and symptoms that may indicate a certain disease.
Bias
Any systematic error in the design, conduct and analysis of a study that results in a mistaken estimate of an exposure’s effect on the risk of disease (or the outcome).
Systematic
Done according to a fixed plan, methodical.
Validity
The absence of systematic bias in results.
Internal validity
The ability to make unbiased inferences about the association of interest in the study population. “The ability to get the right answer.”
External validity
The ability to make unbiased inferences about the association of interest to populations beyond the source population.
Confounding bias
Occurs when the observed association between the exposure and outcome is mixed up with a third factor. Occurs when a true counterfactual state is not achieved.
Epidemiologic triad
Interaction between host, agent and environment to cause disease
Primary or definitive host
A host in which the agent reaches maturity and, if possible, reproduces sexually
Dead-end or incidental host
A host in which the agent is not able to transfer to the definitive or primary host, preventing the agent from completing its lifecycle. An type of intermediate host.
Amplifying host
A host in which the level of the agent can become high enough that a vector that feeds on it will probably become infectious.
Secondary or intermediate host
A host that harbours the agent for a short transition period, during which some developmental stage may be completed.
Primary prevention
Prevent exposure to the the causal factor
Secondary prevention
Detect disease before clinical disease occurs.
Teritary prevention
Diagnose and treat clinical disease
Incidence
The number of new cases in a defined population during a specific time period
Prevalence
The number of cases in a defined population at a point in time, or period of time.
Horizontal transmission
Transmission from one host to another, either directly or indirectly through an intermediate host or vector
Vertical transmission
Transmission from mother to child, in utero, in ovo, and via milk
Infectivity
How many organisms are required to cause disease
Virulence
The ability of an organism to cause disease or damage to the host
Communicability
The time in which the disease can transfer from one individual to another.
Reservoir
Any person, animal, arthropod, plant, soil or substance (or combination of these) in which an infectious agent normally lives and multiplies, on which it depends primarily for survival, and where it reproduces itself in such manner that it can be transmitted to a susceptible host
Carrier
A person or animal that harbors a specific infectious agent without discernible clinical disease and serves as a potential source of infection. May be short or long duration.
Incubation period
Time from exposure to start of clinical disease.
Latent period
Time from exposure to pathological changes in the host.
Sensitivity
The proportion of diseased individuals that test positive. The probability of detecting a disease positive individual with the test. The proportion of true positives that are correctly identified by the test.
Specificity
The proportion of disease negative individuals that test negative. The probability of detecting a disease negative individual with the test. The proportion of true negatives that are correctly identified by the test.
False positive fraction
The proportion of disease negative individuals that test positive.
False negative fraction
The proportion of disease positive individuals that test negative.
Positive predictive value
The proportion of test positive individuals that are truly diseased. A measure of how useful a test is when applied to individuals with unknown disease status.
Negative predictive value
The proportion of test negative individuals that are truly disease free. A measure of how useful a test is when applied to individuals with unknown disease status.
