EPI Final Exam Flashcards
How to Calculate Prevalence Period
existing cases at start + new cases over a period of time/ size of population at start of time period = %
How to calculate prevalence point
existing cases at “point” in time/ size of population at “point” in time = %
a single point in time
how to calculate incidence proportion (cumulative incidence= CI)
number of people developing the outcome/ number of people at risk
CI=IR x time
estimation for risk in a population “at risk” (candidate population)- fixed population
how to calculate incidence rate (IR)
number of people developing the outcome/ total time at risk
estimates change in risk over time in a population at risk- fixed or dynamic population (instantaneous risk)
how to calculate incidence density
number of new cases / sum of the person-time of the at-risk population
how to calculate person time incidence
the number of new cases/ person time at risk through observation
how to calculate crude death rate
number of death in a given period/ the population exposed to risk of death in that period
how to calculate proportionate mortality
number of deaths from a given cause in a specific period of time/ total number of deaths in the same period
how to calculate case fatality rate
proportion of individuals with a disease who die from the disease
what is age adjustment
standardization
- provides a valid comparison using a single number for each population
- transform a measure based on a specific factor composition of a reference population
- referred to as the direct method of standardization
why is age adjustment used
almost all diseases occur at different rates in different age groups, so for accurate analysis- its going to be important to take this into account
what are age specific rates
total number of health events for the specific age group of interest/ total population in that age group
how are age specific rates used
multiplying the age-specific rates of disease by age- specific weights
what is the formula for risk difference/excess risk
Re-Ru/Ru = RR -1 (expressed as percent
the null value is 0%
not a proportion just a ratio
“relative risk”- often described as the percent change relative to the reference risk
what is the formula for risk ratio
RR = Re/ Ru
Risk ratio & rate Ratio
Rate Ratio : Rr = IRe/ IRu
Prevalence ration = Pe/Pu
what is the formula for odds ratio
(a/b)/ (c/d) or ad/bc
what is the formula for relative risk
deaths or disease risk in a specific population/ risk of people from all other groups
how do you calculate and interpret risk difference/excess risk
RE-Ru/Ru = RR -1 (expressed as a percent)
- increase linearly above one and exponentially below one
RR= Rm/Rf and RR = Rf/Rm
how do you calculate and interpret risk ratio
no effect (null value) is 1.0 RR >1 indicates GREATER risk for exposed population relative to reference population
RR < 1 indicates lesser risk for exposed population relative to reference population
how do you calculate and interpret odds ratio
odds of the first group/ odds in the seconds grouphow
how do you calculate and interpret relative risk
death or disease risk in a specific population/ risk of people from all other groups
definition of attributable risk
amount of proportion of incidence of disease or death in individuals exposed to a specific risk factor
definition of population attributable risk
risk in the total population that would not have occurred if exposure had not occurred )may also be expressed as number of cases)
PRD = R total - Ru
what type of epi study uses case control sutdies
main features:
- individuals with the outcome are identified (cases)
- individuals without the outcome are identified (controls or referents)
- exposure is determined for cases and controls at an appropriate time IN THE PAST (there is no follow-up)
- the association between exposure and health outcome is quantified using the odds ratio
what type of epi study uses cohort studies
population with one or more common characteristics or experiences
experimental (intervention) studies
Observational Cohort Studies
- prospective cohort
- retrospective cohort
what type of epi study uses ecological studies
data representing entire populations are used to evaluate an association
exposure status and outcome status are single values applied to the entire population
correlations can be positive, negative, or zero
may not represent the association that exists on the individual level (ecological fallacy)
more complicated relationships can be masked
what type of epi study uses cross sectional studies
Assess prevalence of population in characteristics at a “point in time” this means information on current status is collected from a participant only once (no follow up)
information on individuals associations but lacks temporal relationship between :exposure” and outcome
measure of association is the odds ratio (not an estimate of RR for cross-sectional studies)
classified by whether the data is provided by participants for come from an evaluation - interview or examination
conditions to use a case control study
exposure data are difficult or expensive to obtain
small number of participants
disease is rare
disease has long induction and latent period
little is known about the disease
conditions to use a cohort study
good evidence is needed for risk factor
exposure is rare
desire accurate measurement of exposure
little is known about the exposure
limitations: expensive, long time commitment
conditions to use an ecological study
One of the least valid
data representing entire populations are used to evaluate an association
exposure status and outcome status are single values applied to the entire population
correlations can be positive, negative, or zero
may not represent the association that exists on the individual level (ecological fallacy)
more complicated relationships can be masked
conditions to use a cross sectional study
Almost the least valid
strengths: inexpensive and quick , generalizability , useful for public health planning
limitations: prevalence is the measure of disease frequency, not time separation between exposure and outcome, data are prone to bias and often self reported
death rate
number of people dying from a condition in a specified population/ number of people in the specified population = deaths per 100,00
What is external validity
the relevance of internally valid study results to populations with characteristics different from the source population, also called generalizability
What is internal validity
the extent to which studies result represent the true association between a factor of interest and the health-related outcome for the source population
What is the major differences between internal and external validity
When the goal of the study is to evaluate a potential association between a factor and health related outcome, there are two types of validity
when the goal of the study is to estimate a characteristic of a source population, then there is onyl one validity
What is systematic error
always results in bias
what is random error
may result from bias for an individual measurement but not necessarily an average measurement
what is included under systematic error
misclassification, information, selection
what is confouding
mixing of effects between a factor of interest, a health outcome, and a third factor that is a risk factor for the health outcome of interest, but is not of interest in the study. This third factor is often referred to as a confounder
what are the 3 criteria for confounding
- variable must be a risk factor for the outcome in BOTH the exposed and unexposed populations
- the potential confounder must be associated with the exposure in the population that produced the cases
- the confounder can not be an intermediate step in the causal pathway between the factor of interest and the health outcome
what is selection bias
bias that occurs at the selection of participants
what is information bias
incorrect portrayal or records of information or calculation
what is misclassification bias
individual is assigned to a different category than they should be
What are the strategies to control confounding
randomization restriction matching stratification adjustment multivariate analysis
What is used to reduce bias
placebo- pharmacologically inactive substance given as a substitute for an active substance
sham procedure-bogus procedure designed to resemble a legitimate procedure
blinding- withholding idtentiy of group assignment
what is confounding ( direction away, towards the null)
occurs when risk factors for the outcome, other than that being studied distorts the measures association between the factor being studied and the outcome
What is matching
selection of unexposed subjects that have characteristics identical to cases
What sets the data towards the null (ex)
ex. CRUDE RR = 1.5
Adjusted RR = 2.5
CRUDE less than
negative confounding-bias towards the null
What sets the data away from the null (ex)
ex. CRUDE RR= 3
Adjusted RR = 2
CRUDE larger
positive confounding- bias away from the null
Define sensitivity
proportion of people with the disease who have also a positive result for the test, sign, or symptom.
this is a measure of the ability of a screening test to correctly identify people WITH the outcome of interest
Define specificity
the proportion of people among those who do not have the disease who also have a negative result for the test, sign, or symptom.
This is a measure of the ability of a screening test to correctly identify people WITHOUT the outcome of interest
Define negative predictive value
proportion of people with a negative test results who actually do not have the outcome of interest- measures accuracy of negative test results
define positive predictive value
proportion of people with a positive test result who actually have the outcome of interest- measure of the accuracy of a positive test result
what is a p-value
the probability the point estimate based on data would be as far from the null hypothesis or farther than that actually obtained - probability of a false positive conclusion
how do you interpret a p-value
p value LESS than a predetermined cutoof is taken to indicated as “statistically significant” result
most typical cutoff is p = .05
Null hypothesis is true, do not reject - correct
Null is true, rejct - type 1 error (fals pos)
Null false, do not reject - type 2 error (false neg)
Null false, reject- correct
what is an epidemic
increase in disease frequency of a disease above what is normally expected in a given population and area
what is an endemic
constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area. Hyperendemic refers to persistent high levels of disease occurrence
what is a pandemic
an international epidemic
what is the difference in epidemic, endemic, and pandemic
epi is in a given area
pan is worldwid
end is a geographic area
Who is included in “externally valid”
entire Us population, reference target popualtion, source population
Null hypothesis: Ho
assumed value or preconceived notion for a population parameter (usually the null value for the RR or OR is =1)
what is infectivity
capacity of an agent to enter and multiply in a susceptible host
what is virulence
capacity of an agent to produce a sever outcome course the most severe outcome would be death
what is antigenicity
capacity of an agent to induce antibody production in a host
what is pathogenicity
capacity of an agent to cause disease in the infected host
what are the types of transmission
direct or indirect
what is reproductive number
r= 1 correspond to constant disease
r> 1 corresponds to increased disease
r<1 corresponds to reduced disease
empirical measure that allows comparison of epidemic potential for different infectious disease under different conditions
what is vector born transmission
indirect infectious agent is conveyed to a susceptible host by some form of living organism called a vector
Alternative Hypothesis Ha
the opposite or complement of the null hypothesis- usually not one but could be greater or less than
Direct transmission
immediate transfer of an infectious agent from an infected host or reservoir to a susceptible host
airborne, direct contact, bites
indirect transmission
vehicle borne, vector born
indirect transmission
vehicle borne, vector born
Type of carriers
inapparent
incubating
convalescent
chronic
inapparent carrier
individual that is infectious in the absence of symptoms throughout the course of their infection
incubating carrier
an individual that is infectious during the incubation period
convalescent carrier
an individual that has recovered from disease but remains infectious
chronic carrier
an individual continues to harbor the viable organism indefinitely and remains infectious to others
chronic carrier
an individual continues to harbor the viable organism indefinitely and remains infectious to others
Active Immunity
attained naturally by infection or immunization
passive immunity
attained naturally but WITHOUT infection
validity =
accuracy
reliability=
precision
reliability=
precision
true or false: the purpose of screening is to identify symptomatic cases of disease
false
true or false: screening is conducted in order to reduce morbidity and improve survival
true
true or false: the positive predictive value is more influence by the specificity than the sensitivity of the screening test
true
true or false: the positive predictive value is more influence by the specificity than the sensitivity of the screening test
true
In the definition of epidemiology, the phrase “determinants of disease frequency in human population” refers to which of the following
WHY it is occuring
A study of retirees from a large manufacturing facility found that the average age death among the retirees was greater than the average age death for the general population. What is the best interpretation of this finding
the comparison is not valid because the general population contains many individuals that die young
Who created the life table
John Graunt
John Snow’s investigation of cholera epidemic in the mid 19th century was an example of which advance in the history of epi?
disease etiology can be investigated in natural experiments
Who observed that during the 1918 influenza pandemic, young adults were at greater risk of dying from influenza if they became infected than were middle age adults
wade hampton frost
What is one reason why randomized clinical trails were developed in the mid 20th century
to improve the assessment of efficacy and safety of drug vaccines
What is one reason why randomized clinical trails were developed in the mid 20th century
to improve the assessment of efficacy and safety of drug vaccines
When a single agent can cause multiple different adverse health outcomes and a particular adverse health outcome can be the result of several distinctly different factors, this is referred to as lack of ____
specificity
Why is it difficult to accurately estimate the average induction and average latent period
the start of disease can’t be determined
in the causal model for the natural history of disease during the___ period the disease process has already started
latent
in the causal model for the natural history of disease, the time from the first action of component cause to development of disease is call the ____ period
induction
a _____ cause is all that is needed for disease to occur
sufficient
a _____ cause must always be present, but may require additional factors to cause the outcome
necessary
Which of hill guidelines for causality comes closest to being a requirement for causality
temporality
several different epi studies on diabetes as a risk factor for dementia found similar results. This support which causality guidline
consistency
Hill guidelines for causality _____ would be satisfied is the effect of exposure increased as the exposure level increased
biological gradient
the relationship between the flu virus and the flu could be used as an example of which of the guidelines for causality
specificity
