Epidemiology Vocabulary Flashcards

Terms Definitions




Local Infection
Suspect case
unexplained symptom
Edgar Sydenstricker
Morbidity (cross-sectional)
validity is aka
American Public health association
Characteristics of Epidemiology
-Population focused
-control of health problems
types of observational studies
cohort (prospective and retrospective)
transmitting/any agent (person or animal or microorganism) that carries and transmits a disease
Both microbes and humans(host) benefitEx. E. coli in gut produces vitamin K that is used by our body
does specificity affect yield
measures how quickly something happens
denominator includes a measure of time.
Causal "guidelines" suggested by Sir AB Hill: Step five
Biological gradient

A “dose-response” relationship between exposure and disease. Persons who have increasingly higher exposure levels have increasingly higher risks of disease.

Example: Lung cancer death rates rise with the number of cigarettes smoked.

Some exposures might not have a "dose-response" effect but rather a "threshold effect" below which these are no adverse outcomes.
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.
Experimental Epidemiology
Planned experiments to control influence of extraneous factors among those exposed to an etiological factor (animals or volunteers).
Symptomatic period
Time during which symptoms present
Compute summary estimate that is mathematically manipulated to account for differential distributions of the confounder across 2 populations – creates ‘comparable’ rates/risks used primarily for age distributions in populations
Key feature of analytic epidemiology
Comparison groups
Conduct involves?
Securing appropriate clearances & approvals, adhering to appropriate ethical principles, abstracting records, tracking down & interviewing subjects, collecting & handling specimens, & managing data.
Cohort study?
Epidemiologist records whether each study paticipant is exposed or not & tracks participants to see if they develop the disease of interest.
-Differs from experimental b/c investigator observes rather determines participants exposure status.
Define Effect
difference in disease occurrence between two groups which differ with respect to a particular exposure
Vitamin B9
Birth defects (neural tube defects)

Possible decrease in seizure threshold
Disease frequency measures...
-Cumulative incidence
-incidence rate
In which type of probability distribution does it specify all possible outcomes of the random variable along with the probability that each will occur?
Mycoplasma pneumoniae
respiratory, crowded conditions, close contact
infectious agents on exterior surface of the body/object
an elevated occurrence of a disease accross a wide geographic area, affecting a substantial proportion of a population.
Occurrence of group of illness similar in nature within a given geographic region in excess of normal expectancy
capacity of agent to enter and multiply in a susceptible host



of new cases of a disease in a population at risk during a specified time
The habitat in which the agent normally lives, grows and multiplies. Can be a human, animal or environment)
the residual effects of an intervention that can occur in a cross-over study during the period after the intervention has been completed
carryover effects
Incubation period?
Stage of subclinical disease extending from time of exposure to onset of symptoms for infectious diseases
1. the ability to produce clinically apparent illness
2. the percentage of infections that result in illness
Eliminate known and unknown sources of bias
True or False:
The more sensitive the test, the better the negative predictive value.
Ability of test to correctly identify those who DO have the disease, as compared to the gold standard test.

Sensitivity = TP/(TP + FN) or a/(a+c)

4-square: top row ab(TP:FP), bottom row cd(FN:TN)
FN=false negative
tested negative, but had the disease
Observational studies can be classified as either ___ or ____
descriptive or analytical
Who was the father of clinical epidemiology?
T/F: cohort studies are suitable for rare diseases
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.
measure of association
A quantified relationship between exposure and disease; includes relative risk, rate ratio, odds ratio.
observation bias
clinical may look harder for improvement in group five the exp(new treatment) b/c he/she thinks it should work better. result response of patients recieving the new treatment is biased towards a good outcome.
Clinial trail
an experimental study that is designed to compare the theraputic benefits of two or more treatments.
Experimenter Bias (Rosenthal effect)
Experimenter knows how participants are expected to respond and may unwillingly coach them to respond in particular way
Carrier definition
Carrier: Individual who harbors the organism but is NOT infected, as measured by serologic studies or evidence of clinical illness.
Secondary Attack Rate
new cases among contacts of primary/given time over total # of contacts times 100
what is a fomite?
inanimate object that transmits disease (clothes, desk, door knobs, etc)
Proportionate mortality
Proportion of deaths in a specified population during a period of time that are attributable to different causes. Each cause id expressed as a persentage of all deaths, and the sum of the causes adds up to 100%
Relative risk formula:

RR = ?
RR = CI(Exposed)/CI(not exposed)
placebo effect
the tendency for those receiving a treatment to experience beneficial effects even when the treatment has no known therapeutic value.
incidence rate
the measure of occurrence of disease per unit time

(always has time in the denominator)

(individuals contribute different amounts of time at risk)
how close the results are to the actual true value
what is yield
the amount of previously unrecognized disease is diagnosed and brought to treatment as a result of the screening
Selection bias
animals not randomized with respect to treatment with topical flea control product
Mortality rates can serve as measures of disease _____ and can help us to determine whether the treatment for a disease has become more _____ over time.

Mortality rates may serve as surrogates for ____ rates when the disease being studied is a severe an
severity; effective



Secondary prevention
activities are aimed at early disease detection
To be effective, a test must be valid
(measures what it purports to measure)
Predictive Value (negative)
P [No diesease/ - negative test]

What is:
True positive/All who tested positive
Positive predictive value
What is the occurrence in a community or region of cases of an illness, specific health-related behavior, or other health-related events clearly in excess of normal expectancy?
host factor
An intrinsic factor (age, race, sex, behaviors, etc.) which influences an individual's exposure, susceptibility, or response to a causative agent.
Which disease can vary by state for reporting?
case rate fatality - the number of clinical cases of disease/# of infected animals. measure of virulence
What is epidemiological surveillance?
It is the ongoing systematic collection, analysis and interpretation of health data that is essential for planning, implementation and evaluation of PH practice. This is closely integrated with a system for the timely dissemination of data.
What is Antigenicity?
Antigenicity: Ability of agent to induce antibody production in the host (e.g. re-infection with measles virus is very rare). The related term “immunogenicity” refers to infection’s ability to produce specific immunity.
Dichotomous variables
make a 2-way choice; they are ratios, proportions and rates. [ x/y(10^n) ] x and y are being compared
Secondary prevention:
a. Focus on early detection and fast treatment of disease- the purpose is to cure or slow the progression of disease.
b. Use test to screen:
i. Breast examination
ii. Mammogram
iii. Eye test
iv. Blood test
v. Etc.
a case-control study design in which pair matching is not used; that is, individual cases are not pair matched to individual controls during the selection process. Frequency matching, however, may be used.
unmatched case-control study
necessary cause
necessary to get the disease but not sufficient in itself to cause it (ex. Cholera)
detection bias
a bias that changes because the follow up was more intense
Using group-level associations to make conclusions about individual-level associations
(for example, association found when national salt consumption and national heart disease levels are compared across countries cannot be used to say eating more salt le
Ecological Fallacy (Aggregation Bias)
Occurrence of disease can be measured using ____, which tell us how fast the disease is occurring in a population and ____ which tell us what fraction of the population is affected.

Because the incidence rate is a measure of the transition from a _____
rates; proportion

non-diseased; risk

risk; potential
Types of analytical studies
1 Case-control studies
2 Cohort studies
advantages of an ecologic study
quick, simple and inexpensive
good method to generate hypotheses if disease etiology is unknown
What are the stages of disease?
1. Clinical
2. Non-clinical
--persistent (chronic)
Pierre Charles Luis
father of epidemiology - first real systematic numerical analysis of study - biostatistics - taught many future important figures
What is the elementary kind of sampling where each person has an equal chance of being selected out of the entire population?
Simple random sampling
attack rate:
A variant of an incident rate, applied to a narrowly defined population observed for a limited period of time, such as during an epidemic.
dot plot
A visual display of the actual data points of a noncontinuous variable.
Formula for odds
probability of event / (1-prob of event)
probable case
Acute onset of 3 of the 4 known symptoms of a disease
point prevalence rate
# exist cases during specific point of time/ total midpoint population at risk
5 W's of descriptive epidemiology
What, who, Where, When and Why/how
Definition of incidence proportion
The proportion of an initially disease free population that develops disease, becomes injured or dies during a specified period of time.
What is a single blind study?
Placebo-controlled study where the subjects are blind but investigators are aware of who is receiving the active treatment.
Epidemic period time graph?
Shows time course of disease outbreak or epidemic.
-Use a Epidemic curve
(# death from a specific disease/ # cases over same time period) x 10^n
Case Fatality Rate
Predictive value positive test?
stands for the proportion of test postitive animals which really have the disease
limitations of cross-sectional studies
1. do not provide INCIDENCE
(only prevalence)
2. cannot study disease etiology
(incidence-prevalence bias)
3. difficult to study low prevalence diseases
4. cannot determine temporality
What is a control?
Definition: A sample of the source population that gave rise to the cases.

Purpose: To estimate the exposure distribution in the source population that produced the cases.
Study designs can be classified into 2 major categories...
experimental and observational
sex-specific mortality rate
A mortality rate among either males or females.
The probability of not having the condition given a negative test?
Negative Predictive Value (NPV)
What is Attack Rate?
It is a measure of risk. Number affected/number at risk in a specific period of time.
what is Infectivity? give example
Infectivity: Capacity of agent to enter and multiply in a susceptible host (hence produce infection/disease). Ratio of number of persons developing clinical illness/number of exposed individuals. Ex. Polio and measles have high infectivity
5 stages of infectious disease
1 - incubation period2 - Prodronal period3 - period of illness4 - period of decline5 - period of convalence
Incubation period (infectious disease) and latency period (chronic disease)
Time when disease process has been triggered and pathological changes occur without the individual being aware of them.
Person is asymptomatic
Can last minutes or even decades
specificity...word and number
1. the ability of a test to identify correctly those who do not have the disease
2. true negative/all without disease
what is predictive value
the ability of a screening test to predict the presence or absence of a disease depends on...
1. prevalance
2. sensitivity/specificity
Cyclic fluctuations in communicable diseases
U reflect the balance between the pathogen and the herd immunity of the population
what are the 5 criteria for causality based on the surgeon general
consistency upon repetition
strength of association
time sequence
coherence of explanation
What is the definition of Epidemiology?
Study of the distribution and determinants of health-related states or events in specified populations (and application of this study to the control of health problems)
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.
What is period prevalence?
It is the number of events at any point during a period of time.
What are the 2 sampling strategies for Cohort studies?
Population Based & Exposure Based
What is a triple blind study?
Not only are the treatment and research approaches kept a secret for the subjects and investigators, but the analyses are completed in a way that is removed from the investigators.
what are the four types of observational studies?
1. ecological
2. cross sectional
3. case control
4. cohort
Common source Vs. host to host epidemics

-graph trends
common source- source epidemic from the infection of a large number of people from a common source- such as food or water

example) E.coli- drinking water reservoirs were contaminated by cattle feces

host-to-host epidemics- can be initiated by the introduction of one infected individual infecting others in the population.

examples) TB, influenza, HIV

-common source- rapid increase in incidences followed by a rapid decline
-host to host- slow, progressive increase in disease incidences followed by a gradual decline.
Define epidemic attack rate
Rate of (number of people at risk in whom an illness develops) to (total number of people at risk).
What are factors that are increasing prevalence
-migration of ill cases
-emigration of healthy person
-immigration of susceptible case on those wth that potential
-prolongation of life cases w/o cure
-increase in new case occurance
What is mortality rate?
It is a measure of risk. # of deaths/# people in pop at midyear. over a period of time.
Validity of screening test should include what two things
1. The test will actually classify a diseased person as likely to have the condition --> (“sensitivity”).2. The test will actually classify a non-diseased person as unlikely to have the condition -->(“specificity”).
Adv. & disadv. of sensitive case definition?
-Adv: incld. most or all true cases
-Disadv: sometimes incld. other illnesses as well.
what are the four major ways by which disease spreads?
1. direct fecal-oral
2. direct aerosol
3. direct contact with bodily fluids
4. direct skin contact
what are the 4 stages of the natural history of disease?
1. susceptibility
2. presymptomatic (sub-clinical)
3. clinical disease
4. disability
Percent Population Attributable Risk
(Rate in exposed x (RR - 1)) / (Rate in exposed x (RR - 1) + 1) x 100

*usually rate in exposed is given in question.
there are 4 Quantitative Measures of Health Status. which one is Useful for allocation of health resources?
Count: Refers to the number of cases of a disease or other health phenomenon being studied
what is happening at each stage of the disease
1. susceptibility: no disease, risk factors present
2. presymptomatic: no manifest disease, but pathogenic stages started to occur
3. clinic disease: recognizable signs and symptoms
4. disability: onset
what are the four phases of a typical epidemic growth curve?
1. establishment - random effects
2. exponential growth
3. exhuastion of susceptibles
4. equilibrium/endemicity or recurrent epidemics
What are the difficulties in studying chronic diseases.
1. There is no single agent
2. Long latent period
3. Indefinite onset
4. One set of factors are initiators, others are promoters
Who was the first to conduct a RCT?
Pare in XVI century. It was not planned. Tx at the time for wounds (oil) vs a mixture of eg yolk, roses and turpentine.
What are the sequence of a Cohort design?
1. Choose cohort who have factor, but are not ill.
2. Choose comparison group (optional)
3. Track over time to determine disease rates in the two groups
Specificity - what is it and what is the formula?
a=dz with + test; b=false +; c=false neg; d=real neg result. Specificity is the number of TRUE NEGATIVES divided by the number of all people without the disease, probability of a NEGATIVE TEST given that a person does not have dz.
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