WEEK THREE Flashcards
What is epidemiology
-the study of disease patterns and transmission
Epidemiology is concerned w/ the distribution and determinants of health and diseases, morbidity, injuries, disability and mortality in populations
Fields in which epidemiologists have some knowledge of ?
- public health (disease prevention)
- clinical medicine (disease classification and diagnosis)
- pathophysiology (understand basic biological mechanisms)
- biostatistics (quantify disease frequency)
- social sciences (understand social context in which disease occurs )
Who is Barry Marshall
- internist who together w/ collaboration w/ Robin Warren, discovered H. Pylori was consistently present in biopsies from ulcer patients
- started successfully treating patients w/ antibiotics
- won Nobel prize
What is a classic case example of epidemiology?
- cholera
- cause: vibrio cholera bacterium
- mid 19th c. Outbreak in London
- John Snow believed outbreak was spread by contaminated water
Who was john snow
1813-1858
English anesthesiologist who innovated several key epidemiological methods that remain today
“Father of epidemiology”
1900 main causes of death in US
Influenza and pneumonia
Tuberculosis
GI infections
Heart disease
Cerebrovascular disease
1950 main causes of death in US
Heart disease
Cancer
Cerebrovascular
Disease of early infancy
2010 main causes of death in USA
Heart disease
Cancer
Chronic airway disease
What is epidemiological transition
Describes a shift in the patterns of morbidity and mortality from causes related primarily to infectious and communicable diseases to causes associated w/ chronic, degenerative diseases
What is demographic transition
Shift from high birth rates and death rates found in agrarian societies to much lower birth and death rates in developed countries
Define distribution
Distribution implies that diseases do not occur randomly
What are determinants
Factors that can cause a change in a health condition or outcome
What is morbidity
Illness due to a specific disease or cause
What is mortality
Death due to a specific disease or cause
Define endemic
The habitual presence of a disease within a given geographical area
What is an epidemic
The occurrence of an infectious disease in excess of normal expectancy and generated from a common or propagated source
Examples of endemics
Plague among rodents in AZ
Rabies in several animal species in US
Valley fever (coccidioidomycosis) is an endemic in AZ
Examples of epidemics
Upper respiratory infections
Human rabies
Outbreak of vibrio infections following hurricane Katrina
Examples of pandemics
COVID19
1918 influenza
HIV/AIDS
What is a sporadic disease, examples?
Disease occurring singly, widely scattered, not an epidemic or endemic
Human rabies
CJD (creutzfeldt-Jakob disease)
What are the phases of natural history of disease
Preclinical phase
Clinical phase
Exposure to pathogen and biological onset of disease occurs during what phase of disease
Prior to preclinical phase
The preclinical phase begins with the _______ and ends with ?
Preclinical phase begins w/ biological onset of disease and ends when symptoms appear
What occurs during the clinical phase
Diagnosis and therapy begins
Who was Robert Koch?
1843-1910 German physician
- Koch’s postulates demonstrated the association b/w a microorganisms and a disease
What are Koch’s postulates?
- Organism must be observed in every case of the disease
- Must be isolated and grown in pure culture
- Pure culture must, when inoculated into a susceptible animal, reproduce the disease
- The organism must be observed in, and recovered from, the experimental animal
Who was Sir Austin Bradford Hill and what is he known for?
English epidemiologist
Developed Hill’s criteria for causation in 1965
What are Hill’s 9 criteria for causation
- Strength
- Consistency
- Specificity
- Temporality
- Biological gradient
- Plausibility
- Coherence
- Experiment
- Analogy
What is temporality in Hill’s criteria for causation
The cause (exposure) must be observed before the effect
What is biological gradient in Hill’s criteria for causation
- AKA dose-response, shows a linear trend in the association b/w exposure and disease
what is plausibility in Hill’s criteria for causation
The association must be biologically plausible from the standpoint of contemporary biological knowledge
What is the epidemiological triangle
A model used to describe the etiology of infectious diseases
3 major factors: agent, host, environment
Affected by: time, transmission types, vectors of vomîtes
What is a dose response curve
Type of correlative association b/w an exposure and effect
Threshold refers to the lowest dose at which a particular response occurs
Ex: dose-response relationship b/w the # of cigs smoked daily and mortality from lung cancer
What is an epidemic curve
Graphic plotting of the distribution of cases by time of onset
Helps in identifying the cause of a disease outbreak
What is internal validity
The degree to which a study has used methodologically sound procedures
what is external validity
One’s ability to to generalize the results of the study
what is the definition of error
Difference b/w the value obtained and the true value for the population
Two categories: sampling error and non-sampling error
What is sampling error
Variation that occurs because we are studying a sample rather than an entire population
Even if samples are chosen properly and are representative of the population, there will always be natural variation b/w diff samples
Can be quantified
What are measurements to express sampling error
- confidence intervals
- standard error
- margin of error
- coefficient of variance
What is non-sampling error
Errors that are a result of factors other than using a sample
Result in bias
What types of bias may impact epidemiological studies
Bias = systematic deviation of results or interferences form truth
Recall bias
Selection bias
Observer bias
Confounding bias
Can bias be measured
No
How to control for recall bias
Be aware of limitation when selected study method
How to control for observer bias
Blind or double blind
Script
Multiple observers
How to control for selection bias
Randomization
How to control for confounding bias
Design phase: think through professional con founders
Analysis phase: some types of analysis can control for confounders
The field of descriptive epidemiology classifies the occurrence of disease according to what variables
Person (who is affected)
Place (where condition occurs)
Time (when and over what time period condition has occurred)
What is a case report
In depth study of one case
No comparison group
what is a case series
Three or more cases involving patients given similar treatment
No comparison group
What is a cross-sectional study
- Looks at data at a single point in time
- Participants are not selected based on outcome or exposure, just based on inclusion/exclusion criteria
what is an ecological study
A special kind of cross-sectional study
- units of analysis are populations or group of people rather than individuals
What are some examples of ecological studies
- incidence of disease post vaccination programs
- how tobacco taxes affect tobacco use
- certain occupations and hearing loss
- cancer rates and dietary practices
What is ecological fallacy
Associations observed at group level do not necessarily hold true at the individual level
“ there are both high levels of toxic pollution and cancer in norther NJ, therefore toxins are causing cancer”
Is an example of…?
Ecological fallacy
What does COUNT refer to as an epidemiological measure
Refers to the number of cases of a disease or other health phenomenon being studied
What is a proportion
Comparison of a part to the whole
Type of ratio in which the numerator is part of the denominator
Application: proportion of deaths among men, proportion of lung cancer due to smoking
Ex: arrack rate, point prevalence
What is a rate
Compares two numbers
-measure of frequency where event occurs in a defined population over a specific period of time
- way of standardizing in order to make a fair comparison
What is population at risk
Members (human or animal) of the overall population who are capable of developing the disease of condition being studies
Usually identified as the denominator in rate calculation
What are the 3 types of rates
Crude rate
Specific rate
Adjusted rate
What is crude rate
Summary rate based on the actual number of events in a population over a given time period
*incidence, prevalence, morbidity, mortality
What is specific rate
Based on a particular subgroup of the population defined
*cause, age, proportional mortality rate
What is adjusted rate
Measures where statistical procedures have been applied to remove the effect of differences in population distributions
- standardized mortality rate
What does prevalence measure
The number of affected persons
Number of persons w/ disease of interest
Number of cases/number of people in the population
What is incidence
Number of new cases of disease during a specified time period
Number of new cases/number of persons in population
What are factors that cause prevalence to increase
- increases in incidence
- longer duration of the case
- in migration of cases
- prolongation of life patients w/out a cure
What are factors that cause prevalence to decrease
- decreases in incidence
- shorter duration of disease
- influx of healthy people into population
- improved cure rate
What is the numerator and denominator of morbidity rate
Numerator = total # of illnesses in a population over a specialized period of time
Denominator = average population at risk over same time period
What is the numerator and denominator of mortality rate
Numerator = total # of deaths in population over a specified time
Denominator = average population at risk over same time period
What is the direct method of adjusted rates
Used when you know the age-specific rates of mortality or morbidity in all the population under study
What is the indirect method of adjusted rates
Only need to know the total number of deaths or cases and the age structure of the study population
Preferable when there are small numbers in particular age groups
What are limitations associated w/ adjusted rates
Adjusted rates are artificially created so they can
- lead to misinterpretation
- based on assumptions
- should only be compared to another rate that was computed the same way
What is descriptive analytical epidemiology
- used when little is known about the disease
- relies on preexisting data
- who, when, where
- illustrates potential associations
What is analytical epidemiology
- used when insight about various aspects of disease is available
- rely on development of new data
- why
- evaluates the causality of associations
What is the Odds Ratio
Measure of the association b/w exposure and outcome in CASE CONTROL STUDIES
provides a rough estimate of relative risk
what is relative risk
used when comparing outcomes of those who were exposed to something vs those who were not exposed
used in cohort studies and randomized clinical trials
what is a cross over study
groups get switched, reduces variation b/w groups
what is a community trial
looks at how intervention affects the population in the community
–> behavioral change at the population level
ex: water fluorination
smoking cessation campaigns
what does an Odds Ratio (OR) = 1 mean
exposure doesn’t affect odds of outcome
what does OR >1 mean
exposure is associated w/ higher odds of outcomes
what does OR < 1 mean
exposure is associated w/ lower odds of outcome
what is sensitivity
% truly positive (a/a+c)
what is high sensitivity?
high confidence that an animal w/ a negative test does NOT have the condition
can trust that negative test result b/c false negatives are low
what is specificity
% truly negative (d / b+d)
what is high specificity?
high confidence that an animal w/ a positive test result actually has the condition
how can sensitivity be improved?
parallel testing = running different tests simultaneously
(+) if either or both tests are positive
( - ) if both tests -
proves you DONT have the disease
how can specificity be improved?
serial testing: running one test after another
- run screening tests then a confirmation test
if confirmation test is +, disease present
if confirmation test is -, test is negative
proves you DO have the disease
what is positive predictive value
what are the chances a positive result is truly +
as disease prevalence decreases, positive predictive value also decreases
Likelihood ratio
incorporates the probability that the test is positive in patients w/ and w/out the disease
what is a positive likelihood ratio
probability that the test is (+) in patients w/ disease / prob. that test is (+) in patients w/out diseasse
what are the 2 models for multifactorial causality?
- epidemiologic triangle
- web of causation
when assessing disease association and causality, how can chance be ruled out
statistical procedures may be used to employ the degree to which chance may have accounted for association
but chance can never be completely ruled out
what plot type is this
dose response curve
what plot type is this
epidemic curve
aids in identifying the cause of outbreak
what type of error results in bias
non-sampling errors
is bias typically more prevalent in analytical or descriptive studies
analytical
