Epidemiology Final Exam Flashcards
Incidence Proportion
of new cases of disease during specified time interval / Population at risk at start of time interval
Synonyms for Incidence Proportion
1) Attack Rate. 2) Risk 3) Probability of developing disease 4) Cumulative incidence
Secondary Attack Rate
of new cases among contacts / (# of people at risk-primary cases)
Incidence Rate
of new cases of disease during specified time interval/ summed person-years of observation or average population during time interval
Point prevalence
of current cases (new and preexisting) at a specified point in time / Population at the same specified point in time
Period Prevalence
of current cases (new and preexisting) over a specified period of time/Average or mid-interval population
Crude Death Rate (Crude Mortality Rate)
Total # of deaths during a given time interval/Mid-interval population
Cause-Specific Mortality Rate
of deaths assigned to a specific cause during a given time interval/Mid-interval population
Proportionate Mortality
of deaths assigned to a specific cause during a given time interval/Total # of deaths from all causes during the same time interval
Death-to-case Ratio
of deaths assigned to a specific cause during a given time interval/# of new cases of same disease reported during the same time interval
Neonatal mortality rate
of deaths among children< 28 days of age during a given time interval/# of live births during the same time interval
Postneonatal mortality rate
of deaths among children 28-364 days of age during a given time interval/# of live births during the same time interval
Infant mortality rate
of deaths among children< 1 year of age during a given time interval/# of live births during the same time interval
Maternal mortality rate
of deaths assigned to pregnancy-related causes during a given time interval/Number of live births during the same time interval
Age-Specific Mortality Rate
of deaths of people in a particular age group/# of people present in the age group
Sex-Specific Mortality Rate
of deaths males OR females/ # of males OR females
Race-Specific Mortality Rate
of deaths among people in particular race category/# of people in particular race category
Case Fatality Rate
of cause specific deaths among incident cases/ total # of incident cases
infectivity
of people infected/ # of people exposed
Pathogenicity
of people who develop clinically apparent disease/ # of people infected
Virulence
of people who die/ # of people who develop clinically apparent disease
Attributable Risk % (AKA attributable risk reduction ARR)
(# case in exposed/total # exposed) - (#cases unexposed/total # unexposed)
Control Group Rate/Risk (CGR)
of events in control group/total # of control participants
Experimental Group Rate/Risk (EGR)
of events in experimental group/total # of experimental participants
Attributable Risk Reduction
Control Group Rate (CGR) - Experimental Group Rate (EGR)
Relative Risk
EGR/CGR
Relative Risk Reduction (RRR)
1) (CGR-EGR)/CGR
2) 1-(EGR/CGR)
3) 1-RR
*Note: all 3 formulas should give you the same result
Epidemiology
The study of the distribution and determinants of health-related states or events in specified populations and the application of this study to control of health problems
Etiology
The cause of a disease
Primary Prevention
Action taken to prevent the development of a disease in people who do not have the disease Examples: Vaccines, healthy behaviors, etc.
Secondary Prevention
Identifying people in whom a disease process has already begun but who have not yet developed clinical signs or symptoms of the disease (preclinical phase) Examples: Cancer screening, mammograms, etc.
Tertiary Prevention
Preventing complications in those who have already developed signs and symptoms of an illness and have been diagnosed (those in the clinical phase of illness) Examples: Cancer treatment, physical therapy, etc.
Direct Transmission
Disease is transmitted from person to person by direct contact. Examples: STIs
Indirect Transmission
Disease is transmitted from person to person by a common vehicle like contaminated air or water or a vector. Examples: yellow fever (mosquitos), Lyme Disease (ticks), etc.
Disease
any harmful deviation from the normal structural or functional state of an organism, generally associated with certain signs and symptoms and differing in nature from physical injury. A diseased organism commonly exhibits signs or symptoms indicative of its abnormal state. There is subclinical or non-clinical (change from normal structure or function) vs. clinical disease (change from normal structure or function expressed via signs/symptoms)
Clinical Disease
Characterized by signs and symptoms
Nonclinical (inapparent) disease
Signs and symptoms have not developed. Includes preclinical, subclinical, persistent, and latent disease.
Preclinical disease
Disease is not clinically apparent but is destined to progress to clinical disease
Subclinical disease
Disease is not clinically apparent and is not destined to become clinically apparent. Diagnosed by serologic response or culture of the organism
Persistent (chronic) disease
Disease or infection that can last for many years or even life
Latent disease
Infection with no active multiplication of the agent, only the genetic message is present, not the viable organism
Carrier
Person who harbors the organism but is not infected as measured by serologic studies or shows no evidence of clinical illness
Endemic
The habitual presence of a disease within a given geographic area
Epidemic
The occurrence in a community or region of a group of illnesses of similar nature, clearly in excess of normal expectancy and derived from a common or a propagated source
Pandemic
A worldwide epidemic
Common-vehicle exposure
Cases arise from the same exposure; Example: food poisoning outbreak from bad chicken at a buffet
Herd immunity
The resistance of a group of people to an attack by a disease to which a large proportion of the members of the group are immune
Incubation period
The interval from infection to the time of onset of clinical illness. Often measured as the time from exposure until the onset of clinical disease as it is difficult to determine the exact time of infection.
Epidemic curve
A graph used to characterized the two primary types of outbreaks (common source and propagated). The y-axis is the number of cases and the x-axis is the date of onset each case patient. Note not all epidemics are common source or propagated- for example with some zoonotic or vector borne diseases.
Primary case
A person who acquires the disease from a specific exposure
Secondary case
A person who acquires the disease from exposure to a primary case
Epidemiologic surveillance
The ongoing systematic collection, analysis, and interpretation of health data essential to the planning, implementation, and evaluation of public health practice closely integrated with the timely dissemination of these data to those who need to know
Passive surveillance
Surveillance in which available data on reportable disease are used, or in which disease reporting is mandated or requested by the government or the local health authority, with the responsibility for the reporting often falling on the health care provider or district health officer. Provider initiated; less resource intensive. Also known as ‘passive reporting’
Active surveillance
A system in which staff are specifically contact providers or others to carry out a surveillance program. Often more accurate than passive. Health-department initiated; more resource intensive
Rates
Tell how fast the disease is occurring in the population
Proportions
Tell what fraction of the population is affected
Cumulative incidence proportion
Incidence calculated using a period of time during which all of the individuals in the population are considered to be at risk for the outcome.
Person-time
The sum of the units of time that each individual was at risk and was observed. Often expressed in person-months or person-years.
Prevalence
The number of affected persons present in the population at a specific time divided by the number of persons in the population at that time. What proportion of the population is affected by the disease at that time?
Case fatality
What percentage of people who have a certain disease die within a certain time after the disease was diagnosed?
Direct age adjustment
A standard population is used in order to eliminate the effects of any differences in age between two or more populations being compared. Most commonly used method.
Indirect age adjustment
Used when numbers of deaths for each age-specific stratum are not available or in an occupationally exposed population.
Cohort effect
Changes seen are attributable to the characteristics of the particular ‘cohort’ under study, not the variable being studied.
Evidence-Based Medicine (EBM)
Conscientiously working with patients to help them resolve (sometimes) or cope with (often) problems related to their physical, mental, and social health
Hierarchies of evidence
A system of classifying and organizing types of evidence, typically for questions of treatment and prevention. Clinicians should look for the evidence from the highest position in the hierarchy
Evidence
Any empirical observation, whether systematically collected or not.
Evidentialism
A theory of knowledge that holds that the justification or reason of a belief is determined by the quality of the believer’s evidence for the belief
GRADE (Grading of Recommendations Assessment, development, and Evaluation)
System of rating the quality of evidence and strength of recommendations that is explicit, comprehensive, and increasingly adopted by guideline organizations. Four levels (very low-high).
Secondary evidence-based journals
A secondary journal does not publish original research but rather includes synopses of published research studies that meet prespecified criteria of both clinical relevance and methodologic quality
Background questions
These clinical questions are about physiology, pathology, epidemiology, and general management and are often asked by clinicians in training. The answers to background questions are often best found in textbooks or narrative review articles.
Foreground questions
These clinical questions are more commonly asked by seasoned clinicians. They are questions asked when browsing the literature (e.g., what important new information should I know to optimally treat my patients?) or when problem solving (e.g., defining specific questions raised in caring for patients and then consulting the literature to resolve these problems)
PICO framework
Patient, Intervention, Comparison, Outcome. A method for answering clinical questions
Therapy (foreground clinical questions)
Determining the effect of interventions on patient-important outcomes (symptoms, function, morbidity, mortality, and costs)
Harm (foreground clinical questions)
Ascertaining the effects of potentially harmful agents (including therapies from the first type of question) on patient-important outcomes
Differential diagnosis (foreground clinical questions)
In patients with a particular clinical presentation, establishing the frequency of the underlying disorders
Diagnosis (foreground clinical questions)
Establishing the power of a test to differentiate between those with and without a target condition or disease
Prognosis (foreground clinical questions)
Estimating a patient’s future course
Randomized trial/ Randomized Clinical Trial
An experiment in which individuals are randomly allocated to receive or not receive an experimental diagnostic, preventive, therapeutic, or palliative procedure and then followed up to determine the effect of the intervention
Control groups
A group that does not receive the experimental intervention. In many studies, the control group receives either usual care or a placebo
Observational studies
Includes many study designs that are not randomized such as cohort or case control studies where the exposure to the intervention or disease is not controlled by the researcher
Reference standard/Criterion Standard
A method having established or widely accepted accuracy for determining a diagnosis that provides a standard to which a new screening or diagnostic test can be compared
Random Error
A difference between an observed value and a true value due to chance. It is inherent in all measurements. There will always be some variation in all measurements. When the random error is high, the measurement is less precise and we can be less sure of the value of that measurement.
Bias/systematic error
Sytematic deviation from the underlying truth because of a feature of the design or conduct of a research study. There are many different types of bias such as recall bias, reporting bias, etc.; High levels of bias reduce validity
Lost to follow up
Patients whose status on the outcome or end point of interest is unknown
Risk of bias
The extent to which study results are subject to systematic error.
Random allocation/randomization
The allocation of participants to groups by chance, usually done with the aid of a table of random numbers.
Blinding
Patients, clinicians, data collectors, outcome adjudicators, or data analysts unaware of which patients have been assigned to the experimental or control gorup
Descriptive studies
Studies that find patterns among populations among person, place, and time and are used to develop hypotheses to test
Analytic studies
Hypothesis-testing studies- answer the how and why
Case reports
Descriptive study- a comprehensive, detailed description of one case under observation
Case series
Descriptive study- a comprehensive, detailed description of two or more cases under observation
Ecological studies
Descriptive study- A study of group characteristics; Studying a group of people (for example, everybody in Texas) rather than individuals
N=1 studies
Descriptive study- one person trial; using the same person and comparing the outcome for the person before and after the intervention
Cohort study
Observational study- Two groups, one with the exposure and one without the exposure, are followed over time to determine the occurence of disease in each group; can be prospective or retrospective. Exposure is measured BEFORE the outcome
Case-control study
Observational study- Study involves two groups, one with the disease (cases) and one without the disease (controls), and compares the two groups in respect to previous exposures. Disease is measured BEFORE exposure
Cross-sectional
Observational study- prevalence surveys in which exposure and disease status are assessed simultaneously among individuals in a well defined population
Random assignment (clinical trial)
Experimental study- One group has been assigned randomly to receive an experimental agent or intervention and the other group gets a placebo
Quasi-experimental study
Experimental study- an experiment where the subjects are non-randomly assigned to (or offered) the exposure
Nominal
Categorical(qualitative)-Different categories with no specific rank or significance in rank; dichotomous (only two possible answers)
Ordinal
Categorical(qualitative)-Different categories with specific ranks or significance in rank/levels
Interval
Continuous(quantitative)- equally spaced numerical scale with no true zero point
Ratio
Continuous(quantitative)- numerical scale with a true zero point
Descriptive statistics
Describe the characteristics of the sample of individuals that represent the population from which they came from; ratios, mean, standard deviation, etc.
Inferential statistics
Make inferences or predictions about the whole population from the sample taken of that population; p-values, confidence intervals, point estimates, etc.
Hypothesis (significance) testing
generating a hypothesis about a population parameter and then using sample statistics to assess the likelihood the hyposthesis is true
X variable
What we control or change; independent variable; predictor or exposure
Y variable
What we want to measure; Dependent variable; Response or outcome
Null hypothesis
There is no difference between groups; reject or accept the null
Alternate hypothesis
There is a difference between groups
P-value
What is the probability that the difference observed is due to chance?
Type 1 error
Concluding that there is a difference between two groups when there is not; alpha
Type 2 error
Concluding that there is not a difference between two groups when there is a difference
power
Probability of saying there is a difference when there is in fact a difference between two groups; the likelihood of making the right decision
Point estimate
What is the single value most likely to represent the true difference between experimental and control treatments?
Confidence interval
Given the observed difference between experimental and control groups, what is the plausible range of differences within which the true difference might actually lie?
Historical controls
Comparison group from the past
Simultaneous nonrandomized controls
simultaneous controls that are not selected in a randomized manner
Stratified randomization
Assignment method which first stratifies the whole study population into subgroups with same attributes or characteristics then followed by simple random sampling from the stratified groups
Planned Crossover
Patients are first randomized into two groups and then switched between the groups after a certain time period and again observed for a given time period
Carryover
In a planned crossover design, the effects from the first treatment the subjects are on may carry over and affect the subject during the second treatment
Unplanned Crossover
During the course of the study, patients may unexpectedly crossover to a different treatment group
Factorial Design
Examines how two or more variables (factors) predict or explain an outcome
Noncompliance
Patients agree to be randomized but do not comply with the assigned treatment
Intent to treat
Patients for whom data are available are analyzed in the groups to which they are randomized irrespective of what treatment they received
Absolute risk reduction (ARR)/risk difference
The absolute difference (risk difference) in risks of harmful outcomes between experimental groups (experimental group risk [EGR]) and control groups (control group risk [CGR]); calculated as the risk of harmful outcome in the control group minus the risk of harmful outcome sin the experimental group (CGR-EGR); Used to describe a harmful exposure or intervention
Generalizable
The degree to which the results of a study can be generalized to setting or samples other then the ones studied
Number needed to treat (NNT)
the number of patients who must receive an intervention of therapy during a specific period to prevent 1 adverse outcome or produce 1 positive outcome
Noninferiority trials
Address whether the effect of an experimental intervention is not worse than a standard intervention by more than a specified margin
Equivalence trials
Trials that estimate treatment effects that exclude any patient-important superiority of interventions under evaluation; helpful when determining if one intervention is neither better nor worse than another
Validity
The extent to which an instrument measures what it is intended to measure
Truncated RCTs
Trials stopped early due to apparent harm because the investigators have concluded that they will not be able to demonstrate a treatment effect or because of apparent benefit
N-of-1 Randomized Clinical Trials
Experiment to determine the effect of an intervention or exposure on a single study participant; patient undergoes pairs of treatment periods organized so that 1 period involves the use of the experimental treatment and 1 period involves the use of an alternate treatment
Inclusion criteria
Eligible for the study such as having the disease the treatment will target
Exclusion criteria
Not eligible due to various factors
Efficacy
Does the treatment work under ideal, controlled conditions?
Effectiveness
Does the treatment work like it is supposed to in the real world?
Efficiency
Is the benefit of the treatment worth the cost?
Surrogate outcomes
Proxy measures, outcomes that substitute for direct measures
Composite end points
Aggregate measures that used in combination to measure the effect of a treatment; combination of multiple end points
Superiority trial
Determines the magnitude of increased benefit of the experimental intervention over the standard therapy on effectiveness outcomes
Odds Ration (OR)
It is the ratio of: the odds of an event in the treatment group to the odds of an event in the control group.
The odds ratio tells us how more likely or less likely an event is to happen
An odds ratio = 1 implies that the event is EQUALLY LIKELY in both groups.
An odds ratio > 1 implies that the event is MORE LIKELY in the first group.
An odds ratio < 1 implies that the event is LESS LIKELY in the first group.
Relative Risk (RR)
The ratio of the incidence rate of a disease or health outcome in an exposed group to the incidence rate of the disease or condition in a non-exposed group.
Confounding
A situation in which a measure of association or relationship between exposure and outcome is distorted by the presence of another variable.
Positive confounding-when the observed association is biased away from the null (Inflated Result)
Negative confounding -when the observed association is biased toward the null) (Weakened Result)
Four reasons for RCT limits
1) Unethical to randomize harmful exposure
2) Insufficient power to detect rare and serious adverse events or effects
3) Limited follow-up, not suitable for long-term effects
4) Most RCTs do not provide info on harm
Advantages and disadvantages of Cohort studies
Pros
-good for rare exposures
-reduces bias
-shows temporal relationship
Cons
-Not good for rare diseases
-expensive
-time-consuming
-loss to follow up
Advantages and disadvantages for case-control studies
Pros
-good for several exposures
-good for rare diseases
-less expensive
-no follow up
Cons
-not good for rare exposures
-not good for continuous disease outcomes
Advantages and disadvantages for cross-sectional studies
Pros
-good for examining several exposure-disease relationships
-inexpensive
Cons
-cannot establish temporal relationship
-not good for rare diseases with short durations
Nested case control
A case control study within a large cohort; typically seen with large enrollment studies; Controls are a sample of individuals who are at risk for the disease/outcome at the same time each case of the disease develops
Case-cohort
Same as nested case-control design, except controls are randomly chosen from the cohort at the beginning of the study.
Can study different diseases with same controls because they are not matched with cases
Matching
adjust for possible confounders and gain efficiency (precision); when a case is matched to a control based on a characteristic
CANNOT study ‘matched’ characteristic
Differential misclassification
occurs when the information collected differs for the exposed and non-exposed groups and this difference IS related to the exposure or outcome
Non-differential misclassification
occurs when the information collected differs for the exposed and non-exposed groups and this difference is NOT related to the exposure or outcome
selection bias
In a cohort or experimental study
-when there are differences in participation or selection of participants in the exposed and non-exposure groups and this difference is related to the outcome
In a case-control study
-when there are difference in participation or selection of participants in the cases and controls and this difference is related to the exposure
Information bias
occurs due to errors in the measurement of or collection of data which the distorts the association or measures of association (RR, OR etc.). Misclassification of either the exposure or outcome.
Sample population
people who are in the study
Source population
population eligible to be in the study and are at risk for the outcome
Target population
Population you want to target your results to, generalize your results to
Correlation
A measure of the relationship between two variables
Regression
primary interest, to examine strength relationship between predictor variable and a target (exposure) , dependent variable (outcome). Predictions!
Screening test
Used when people are considered to be at high risk of developing a disease or condition, before the clinical phase (pre-clinical phase).
Diagnostic test
Any kind of medical test performed to aid in the diagnosis or detection of a suspected disease or condition; in the clinical phase.
Sensitivity
True positive rate
SNout- rules out a disease
Ability to recognize and appreciate the personal characteristics of others
a/a+c
Specificity
True negative rate
SPin- rule in a disease
Of those without the disease, what’s the probability they will not be detected by the test?
d/b+d
Positive Predictive Value (PPV)
Helps determine what the probability is that your patient will have the disease given a positive test result
a/a+b
Negative Predictive Value (NPV)
helps you determine what the probability is that your patient will not have the disease given a negative test result
d/c+d
Sequential testing
a screening strategy that uses one test followed by one or more additional tests if the first test is positive
Second test is usually more invasive or risky or expensive and is higher sensitivity or specificity
Gain in specificity, loss in sensitivity
Simultaneous testing
A screening strategy that uses two tests initially if one test is positive then the case is positive
Both tests have to be negative to be considered negative
Gain in sensitivity, loss in specificity
intrasubject variation
variation within individual subjects
intraobserver variation
variation in the reading of test results by the same reader
Interobserver variation
variation between those reading the test results
Critical point
the point at which we can imagine that, before this point, treatment is more effective and less difficult to administer.
can have one or more critical points
Volunteer bias (referral bias)
persons seeking preventative care may be healthier than those showing up for acute problems
type of selection bias
length-biased sampling
So the natural history of disease differs between people and for different diseases and that includes the clinical phase
type of selection bias
Lead time bias
Bias arising from how much earlier a disease can be diagnosed if disease is detected by screening compared with the usual time of diagnosis if screening was not carried out
Over diagnosis bias
Due to screening, people without disease labeled as having the disease (false positives)
Results in increased survival due to screening, but this is an artifact of screening
Pre-test probability
The probability of a patient having the target disorder before a diagnostic test result is known.
Testing threshold
in diagnostic testing, the point at which the optimal decision is to perform a diagnostic test
Treatment threshold
In clinical decision making, the point at which a decision is reached to treat the patient without first performing a diagnostic test.
Post test probability
probability of the disorder once the test results are obtained
Spectrum bias
Difference in those in that participate in the study in terms of disease spectrum compared to the population the test will be applied to
Lack of external validity
Blind assessment
Clinical info + diagnostic test results influences final diagnosis of patient and this differs between the two groups (experimental and standard testing groups)
differential misclassification
Verification/work-up bias
Selection bias
Dependent of the results of one test determines who will receive the confirmatory test
Narrative review
•review article; does not incorporate methods to assess and minimize bias
Synopsis
•summary of a primary study, systematic review, or meta-analysis that includes key methodological details
Systematic review
appraisal of several primary studies to address a focused clinical question; incorporates methods to reduce likelihood of bias
Meta-analysis
•statistical technique for quantitatively combining results of several primary studies addressing the same outcome via a pooled or summary estimate
Paternalistic approach
clinician offers minimal info to the patient about options; makes decision without patient input or consideration of patient values or preferences.
Clinician-as-the-perfect-agent approach
•clinician considers patient’s values and preferences but there is no active involvement of the patient in the decision. Clinician must take careful consideration of being current on patient’s values and preferences- difficult
Informed decision making
•empowering to patients- clinician provides the patient with information and the patient makes the decision; provider serves as an expert in technical aspects
Shared decision making
bidirectional approach in which patient and provider both bring information, evidence, values, and preferences in making a decision.
Power gradient must be minimal and the patient must be reassured that the clinician will act according to the patient’s informed values and preferences even if in conflict with that of the providers.
Team Talk
patient has reasonable options and the physician’s role is to help the patient understand these options and how to consider these options in more detail
Option talk
•provider is clear about reasonable treatment alternatives and helps patient compare them.
Decision talk
•asking patient what matters most to them once they understand and compare them treatment options and alternatives. Helps patient form their own views.
Patient decision aids
based on a systematic review- present information about the disease, treatment options, and potential outcomes in a patient friendly manner- information that is descriptive and probabilistic
Four bioethical principles
Respect for autonomy
Beneficence
Non-maleficence
Justice
Respect for autonomy
•preserving an individuals preferences, rights, dignity- retaining and promoting the ability to determine an individual’s own course
Beneficence
•provider’s responsibility to promote the well-being of others
Non-maleficence
•provider’s responsibility to actively avoid harm or injuring others
Justice
•Fair, equitable, and appropriate treatment in light of what is due or owed to a person
