Epidemiology Flashcards
surveillance
ongoing, systematic collection, analysis, and interpretation of health-related data
goal of surveillance
to provide information to be used for public health action
Must the CDC be invited by a state before conducting public health surveillance?
Yes
Passive surveillance
- diseases are reported by health care providers
- simple and inexpensive
- limited by incompleteness of reporting and variability of quality
active surveillance
- health agencies contact health providers seeking reports
- ensures more complete reporting of conditions
- time consuming and expensive
sentinel surveillance
reporting of health events by health professionals who are selected to represent a geographic area or a specific reporting group
can be active or passive
syndromic surveillance
focuses on one or more symptoms rather than a physician-diagnosed or laboratory confirmed disease
Epidemiology
the study of the distribution and determinants of health-related states or events in specified populations;
- study (scientific, systematic, data-driven)
- distribution (frequency/pattern)
- determinants (causes, risk factors)
- populations (neighborhoods, school, city, state, country, state)
Disease Distribution
analysis of patterns
describes who gets the disease, where people with the disease are located, and how these aspects of disease change over time
endemic
the ongoing, usual level of, or constant presence of a MMD within a given population
epidemic
outbreak or occurrence of a MMD clearly in excess of usual level of expectancy in a defined community or region
pandemic
worldwide epidemic
Ex: HIV; COVID-19
descriptive epidemiology
Answers - Who is getting the disease?
fixed population
permanent membership based on an event
ex: Hiroshima survivors
Transient/dynamic population
membership based on a condition that changes
ex: where you live
counts
of cases
- answers “How many?”
ratio
one number (x) / another number (y)
- can be related or independent
- range 0 to infinity
proportion
type of ratio; expressed as a percentage
numerator is subset of the denominator;
x/(x+y)
range 0 to 1
risk
probability of outcome occurring among at risk population during a time period
a/N
a=# of new onset cases
N = population-at-risk at beginning of follow-up
rate
quantity per unit of time; measures speed at which things happen
range: zero to infinity
ex: heart rate - 60 beats per minute
incidence rate/density
of new cases (incidence) / # of person-time (PT) of observation
ex: 1 case/4.5 person-years
person-time assumption
assumes rate is constant over different periods of time
ex: 100 persons followed for 10 years = 1000 person years
ex: 1000 persons followed for 1 year = 1000 person years
prevalence
proportion;
of existing cases of MMD / # of total population
range 0 to 1
“snapshot”
case fatality rate
not a rate, is a proportion
of deaths from an illness/# of people with the illness
proportionate mortality
the proportion of deaths caused by a specific disease / all deaths
used to determine leading causes of mortality
crude mortality rate
of deaths from all causes / total population in a given time period
cause-specific mortality rate
deaths from a specific cause / total population in a given time period
age-specific mortality rate
of deaths from all causes in a specific age group / # population in specific age group in a given time period
control for confounding by:
- stratification
2. direct standardization
Experimental Study Designs
- RCT
2. Clinical trial
Observational Study Designs
- Case reports/series
- Ecological
- Cross-Sectional
- Cohort
- Case-Control
RCT
compares exposure and outcome among different groups
exposure is randomly assigned by researcher
customary to present patient characteristics table
RCT process
- Identify study population
- randomly assign into 2+ exposure groups
- categorize into outcome groups (e.g. cured/not cured)
Clinical trial limitations
- ethical considerations
- select population (may not be generalized)
- duration (expensive, time consuming)
- adherence (ensuring subjects comply with study procedure)
placebo
ensures control and treatment group have the same “experience”
single blinding
subjects unaware of assigned exposure
double blinding
both subjects and researchers do not know assigned exposure
standard
infant mortality rate
of deaths of infants less than 1 year of age / # of infants less than 1 year of age within a given time period
MMD
Mortality, Morbidity, Disability
incidence
of new cases of disease
disease frequency
how often does the MMD occur in the population?
cumulative incidence (CI)
of new cases of disease / # in at risk population over a specified period of time
estimates the probability that a person will develop disease during a specified time
Cumulative Incidence is used mainly for _____ populations
fixed
incidence decreases + people are living longer with the disease =
increased prevalence
incidence increases + duration is short =
decreased prevalence
incidence decreases + duration is short =
decreased prevalence
relative risk
ratio
rate in exposed/rate in unexposed
relative risk 2x2 table
(a/a+b)/(c/c+d)
odds ratio
the odds that an outcome will occur given a particular exposure; compared to the odds of the outcome occurring in the absence of that exposure
odds ratios are most commonly used in _____, but can also be used in _____ and _____.
case-control studies
cross-sectional and cohort
odds ratio 2x2
(a/b)/(c/d)
-or-
ad/bc
RR is approximate to the OR when:
the disease is rare
ecological studies: unit of analysis
population or groups
ecological studies: exposure status
based on the population
ecological fallacy
making assumptions about the individual based on findings at the population level
ecological studies: time
varies
cross-sectional: time
snap-shot
cross-sectional: population
individual level;
selected without regard to exposure or disease status
cross-sectional: measure
prevalence
cross-sectional: Measure of association
odds ratio
cannot determine cause and effect
case control study
- disease is rare
- disease has a long induction and latent period
- little is known about the disease
case control study: selection of cases based on _____.
outcome
cohort study
- 2+ groups begin disease free
- selection based on exposure
- followed for outcome
- observational equivalent of experimental studies, but unable to allocate exposure
cohort study purpose
studies causes, preventions, and treatments for diseases
randomized control trials
investigate the role of some “agent” in the prevention or treatment of disease
researcher allocates agent
gold standard
goal of randomization
to achieve baseline comparability between compared groups on factors relating to outcome
provides balances with respect to known and unknown factors
The _____ the groups, the _____ randomization works.
larger, better
strategies for increasing compliance?
design
throughout the study
purpose of blinding
to avoid bias in ascertainment of outcome
internal validity
the degree to which
the results are attributable to the
independent variable and not some
other rival explanation
external validity
the extent to which
the results of a study can be
generalized
threats to validity
bias, chance, confounding
chance
random variation
as we _____ the sample size, the impact of chance _____.
increase; decreases
bias
systematic error in the design or conduct of a study;
unintended mistake of the researcher
not affected by sample size
best to control for at the design stage
confounding
not a mistake, but needs to be controlled for
not impacted by sample size
can be controlled for at the design and/or analysis stage
selection bias
systematic error in the method of selecting study participants
misclassification bias
systematic error in the procedures for gathering exposure/disease information
bias leads to:
wrong results leading to misleading conclusions
Dealing with bias at design stage
- subject selection
2. subject/study personnel blinded to subject status
Dealing with bias at data collection
- definitions
- measurements
- standardization
- quality control
confounding
distortion in the measures of the association between exposure and outcome
mixing of effects
association between exposure and disease is distorted
mixed with the effect of another associated factor
Confounding arises when important _____ factors are _____ distributed across groups being compared.
extraneous; differentially
screening
classifies individuals with respect to their likelihood of having a particular disease
potential harms of screening
- false positive
- unnecessary interventions and anxiety
- over-diagnosis
- cost
- discomfort
- embarrassment
WHO recommendations for screenings
- important health problem (prevalence/severity)
- treatment should be available
- available facilities for diagnosis and treatment
- latent stage of disease
- available test for the disease
prevalence
(TP + FN) / total
sensitivity
TP / (TP + FN)
specificity
TN / (TN + FP)
PPV
TP / (TP + FP)
NPV
TN / (TN + FN)
Lowering criterion of positivity results in _____ sensitivity and _____ specificity
increased; decreased
Increasing criterion of positivity _____ sensitivity and _____ specificity.
decreased; increased
for continuous data, the decision for the screening cut point involves weighing the consequences of _____ against _____.
false negatives; false positives
Sensitivity should be increased when _____.
the penalty associated with missing a case is high
ex: very infectious disease
ex: when subsequent diagnostic evals have minimal risk or cost
specificity should be increased when _____.
the costs or risks associated with further diagnostics are substantial.
ex: invasive diagnostics (biopsies)
preclinical phase (Natural progression of disease)
period between developing the disease and symptom onset
clinical phase (Natural progression of disease)
diagnosis, seek care, treatment, outcome
