Exam 2 Flashcards
What are the kinds of descriptive studies
Cross-sectional, single case report, case series, and some ecologic studies
What are the 2 types of analytic studies
Observational and experimental
What are the kinds of observational studies
Case-control, cohort, and some ecologic studies
What are the kinds of experimental studies
Clinical trial and community trial
What are the 3 purposes of descriptive epidemiology
Identify possible health problems, characterize the amount and distribution of health/disease within a population, and generate an etiologic hypothesis
What are the 2 purposes of analytic epidemiology
Identify causes or determinants of health problems and test the etiologic hypothesis
What are the characteristics of experimental design
Controls who is exposed to a factor of interest (Manipulation/M) and assigns subjects randomly to study groups (Randomization/R)
What are the 4 characteristics of clinical trials
Experimental (M and R), tests efficacy of preventative/therapeutic measures, focuses on the individual, and prospective
What are the 4 characteristics of community trials
Quasi-experimental (M only), designed to produce health/behavioral changes in a target population (usually tests health programs, etc.), focuses on community (compares one to another, hard to randomize), and prospective
What kind of calculation can be done for clinical trials
Incidence rates, relative risk, incidence rate ratios, and odds ratio
What is another term for clinical trial
Randomized control trial (RCT)
What are the two types of clinical trials
Prophylactic (prevent disease) and therapeutic (improve health)
What is the timeline of clinical trials
Start with subjects who lack positive history of outcome of interest but are at risk, then include at least 2 time points to determine eligibility/treatment allocation as well as the number of new cases
What is the clinical end point
The outcome of interest in both the intervention and control groups (e.g. rates of disease, death, or recovery)
What is blinding/masking
Single-blind = participants don’t know if they’re intervention or placebo
Double-blind = participants and researchers don’t know if subjects are intervention or control (involves 3rd party)
What are 2 reasons for having phases in clinical trials
To protect public from a potentially deleterious intervention and satisfy the urgent needs for new interventions
What happens in Phase I Clinical Trials
New intervention tested in adult volunteers (usually less < 100 people) –> Must show successful demonstration of response on a small-scale)
What happens in Phase II Clinical Trials
100-200 subjects are selected from the target population for the intervention –> Antibody responses and clinical reactions are examined
What happens in Phase III Clinical Trials
Assesses protective efficacy in target population (at least 1000 people) –> License to manufacture can be granted after this phase
What is efficacy
How does an intervention perform under tightly controlled, ideal situations (compares incident rate of disease in intervention population with control population)
What is effectiveness
How does an intervention perform in the real world
What happens in Phase IV Clinical Trials
Post-marketing research to gather more information about risks and benefits from a drug (effectiveness and safety)
What can community trials help determine
The potential benefit of new policies and programs
What is the timeline for community trials
Determine eligible communities willing to participate, collect baseline measures, use a variety of measures (e.g. disease rates, knowledge, attitudes, and practices), communities randomized and followed over time, and measure outcomes of interest
What is temporality
The timing of information about cause and effect (e.g. did we ask about exposure at the same time, before, or after disease)
What is a cohort
A population group or subset that is followed over a period of time
What are other terms for cohort studies
Prospective or longitudinal studies
What are the basic timelines for cohort studies
Start with patients not positive for outcome of interest but at risk, include at least 2 observation points to determine exposure status/eligibility and number of new cases
What kinds of calculations can be done with cohort studies
Incidence rates, relative risk, incidence rate ratios
What are outcome measures of cohort studies
Discrete events (single events with multiple occurrences), levels of disease markers, and changes in disease markers (rate of change, change in level within time)
What are the 2 kinds of cohort studies
Population-based (exposures unknown until first period of observation when info is collected) or exposure-based (look at exposure first, usually 1:1 ratio)
What is a limitation of population-based cohort vs. exposure-based cohort
They aren’t efficient for rare exposures
What are temporal differences in cohort designs
Prospective vs. retrospective
What are the 3 applications of cohort studies
Studies chronic disease etiology, risk estimation, and hypothesis testing
What is attrition
Subjects lost to follow-up
What are relative measures of effect
Divide disease frequencies from one another (e.g. relative risk, incidence rate ratio, and odds ratio)
What are absolute measures of effect
Subtract disease frequencies from one another (e.g risk difference)
What information is garnered from relative measures of effect
The strength of the relationship between exposure and disease
What information is garnered from absolute measures of effect
The public health impact of an exposure
What are effect measures
A quantity that measures the effect of a factor on the frequency or risk of a health outcome
What is relative risk (risk ratio) and when can it be used
Ratio of risk of disease or death among exposed to risk among the unexposed
What does relative risk tell you
If the risk of disease is different among the exposed as compared to the nonexposed
What is relative risk interpretation
Exposed have X times the risk of disease compared to non-exposed
The risk of disease is X% higher/lower among exposed compared to nonexposed
What is an Incidence Rate Ratio (IRR) and when can it be used
The ratio of incidence rate (uses person time) among the exposed to the incidence rate among the nonexposed
What does Incidence Rate Ratio tell you
If the rate of disease is different among exposed compared to nonexposed
What is interpretation for Incidence Rate Ratios
Exposed have X times rate of disease compared to nonexposed
The rate of disease is X% higher/lower among exposed compared to nonexposed
What is Risk Difference
Difference between incidence of disease in the exposed group and the incidence of disease in the nonexposed group
What is another term for Risk Difference
Attributable Risk
What does Risk Difference tell you
The number of cases of disease that would be eliminated in the exposed group if the exposure was eliminated
What are the 2 measures of potential impact
Etiologic Fraction (Impact of exposure removal on exposed) and Population Risk Difference (Impact of exposure removal on population)
What is etiologic fraction
Proportion of the rate of disease in the exposed that is actually due to exposure
What does etiologic fraction tell you
How much the particular exposure accounts for disease etiology in exposed group
What is population risk difference
Difference between incidence rate of disease in nonexposed part of population and the overall incidence rate in the total population
What does population risk difference tell you
Identifies number of cases of disease that would be eliminated in total pop. if exposure was eliminated (helps see which exposures are most impactful to certain populations to prioritize prevention)
What is “cause”
An event, characteristic, or condition that the disease wouldn’t occur without
What are the 2 types of causality
Deterministic and probabilistic
What is deterministic causality
A cause is always followed by an effect (necessary and sufficient)
What is probabilistic causality
An cause is associated with increased probability of an effect happening (stochastic process)
What are the 4 types of associations
Noncausal, causal, direct, and indirect
What is a noncausal association
A secondary association (B causes D and C causes D, so B and C are not causally associated)
What are the types of causal associations
Direct and indirect
What is an example of a direct association
B directly causes C
What is an example of an indirect association
A causes B which causes C (causal pathway)
What is a case control study
Compares people with disease to people who don’t have disease (cases vs. controls)
What is the purpose of a case-control study design
Looks at whether differences between cases and controls result from exposures to risk factors
What is the timeline of a case-control study
Exposure determined retrospectively, involves just one point of observation
What are the 4 advantages of case-control studies
Smaller sample sizes than surveys or prospective studies, quick and easy to complete, cost effective, and good for rare disease studies
What are the 4 limitations of case-control studies
Unclear the timeline of exposures and diseases (because exposure info was collected retrospectively), indirect estimate of risk, not useful for rare exposures, recall bias
What is a nested case-control studies
Case-control study where both cases and controls are drawn from an existing cohort study
What are the 2 advantages of nested case-control studies
Provide control over confounding factors and reduce cost (because we’re just looking at old data in a new way)
What are odds
The ratio of the probability of an event occurring to that of it not occurring
What is an Odds Ratio
Measure of association between an exposure and an outcome
What does an odds ratio tell you
If the odds of disease are different among exposed as compared to nonexposed
What types of studies can odds ratios be used for
Case-control and RCTs
When are the 3 times when an OR provides a good approximation of risk
When controls are representative of target population, cases are representative of all cases, and frequency of disease in population is small
What are cross-sectional studies
Estimate prevalence of disease within population
What can cross-section studies be used for
To describe magnitude and distribution of a health problem and (with repetition) examine trends in disease or risk factors that vary over time
What are 3 advantages of cross-sectional studies
Generalizability, conducted in relatively short period of time, and low cost
What are 4 disadvantages of cross-sectional studies
Not that useful to infer disease etiology, don’t provide incidence data, can’t study diseases with low prevalence, and can’t determine temporality of exposure or disease (because disease and exposure info collected at same time)
What are ecologic studies
Group analysis usually using secondary data (like census tract) where level of exposure for each individual is unknown
What is the ecologic fallacy
Observations at group level don’t represent exposure-disease relationship at individual level because incorrect inferences are applied to individuals from group data
What is Simpson’s Paradox
Associations observed in subgroups of a population may be reversed in entire population (illustrates confounding)
What are the 4 applications of ecologic studies
Test specific etiologic hypotheses, develop new etiologic hypotheses, suggest mechanisms of causation, and identify new methods for disease prevention
What are 4 advantages to ecologic studies
Quick, simple, inexpensive, and a good approach to generate hypothesis when the etiology of a disease is unknown
What are 2 disadvantages to ecologic studies
Ecological fallacy and imprecise measurement of exposure and disease
What are 4 advantages of cohort studies
Permit direct determination of risk, time sequencing of exposure and outcome, can study multiple outcomes, and can study rare exposures
What are 5 disadvantages of cohort studies
Take a long time, costly, subjects lost to follow up (attrition), selection bias, and difficult to use with rare diseases
What are 2 advantages of RCTs
Provide best control over amount of exposure, timing and frequency of exposure, period of observation, and the ability to randomize reduces the likelihood that groups will differ significantly
What are 4 disadvantages of RCTs
Artificial setting, limited scope of potential impact, adherence to protocol is difficult to enforce, and ethical dilemmas
What is the advantage of community trials
Only way to estimate directly the impact that change in behavior or modifiable exposure has on incidence of disease
What are 3 disadvantages of community trials
Don’t control entrance to study, delivery of intervention, or monitoring of outcomes as well as RCTs, fewer study units can be randomized (not as comparable), and affected by population dynamics, secular trends, and nonintervention influences
What is external validity
For small samples, it implies the ability to generalize beyond a set of observations (study) to some universal statement
What is internal validity
Proper selection of study groups and lack of error in measurement of exposure, outcome, and association between exposure and disease
What is random error
Fluctuations around a true value of a parameter
What 3 factors contribute to random error
Poor precision, sampling error, and variability in measurement
What is poor precision
When factor being measured isn’t measured sharply
What is sampling error
When obtained sample values (statistics) differ from values (parameters) of parent population
What is variability in measurement
Lack of agreement in results due to type of measurement procedure used
How can random error be reduced
Increase sample size and/or number of measurements
What is bias
A systematic error resulting in incorrect (invalid) estimate of measure of association due to error in design, data collection/analysis, interpretation, reporting, and publication
What 4 factors contribute to bias
Observer bias, selection bias, information bias, and confounding
What is Hawthorne (Observer) Effect
Subject’s behavior changes because they know they’re being observed
What is selection/survival bias
When relationship between exposure and disease is different for those who participate and those who theoretically would be eligible but don’t participate
What is an example of survival bias
Fighter pilot plane coming back doesn’t show where armor should be because it made it back
What is the healthy worker effect
Type of selection bias where employed populations tend to have lower mortality than general population
What are 4 techniques to reduce selection bias
Develop an explicit (objective) case definition, enroll all cases in a defined time and region, strive for high participation rates, and take precautions to ensure representativeness
What is information bias
Result of measurement error in assessment of exposure and disease
What are the 3 kinds of information bias
Recall bias, interviewer bias, and prevarication (lying) bias
What is recall bias
Better recall among cases than controls (often people can’t remember the things they did that might have exposed them when they didn’t get sick)
What is interviewer bias
When interviewers probe more thoroughly for an exposure in a case than a control
What is prevarication bias
When subjects have ulterior motives for answering a question so they understate or exaggerate an exposure
What are 6 ways to reduce information bias
Use memory aids to validate exposures, blind interviewers to subject’s status, standardize training sessions and protocols, use standardized data collection, blind participants to study goals, and ensure questions are clearly understood
What is a confounder
An alternate explanation for observed association between an exposure and disease –> Can be controlled for in data analysis
What are the 3 criteria for confounders
Be a risk factor for disease, be associated with exposure, and not be in causal pathway between exposure and disease
What are 3 ways to control confounding
Randomization, restriction, and matching
What are advantages and disadvantages to randomization
+: Convenient, inexpensive, and allows straightforward data analysis
-: Need control over exposure, ability to assign subjects to groups, and large sample sizes
What is the purpose of restriction
To prohibit variation of the confounder within groups
What are the advantages and disadvantages of restriction
+: Gives complete control of known confounders
-: Cannot control for unknown confounders
What are the advantages and disadvantages of matching
+: Fewer subjects needed than in unmatched studies with same hypothesis
-: Costly because requires searching and record keeping to find matches
How can you control confounding through analysis
Stratification and multivariate techniques
What are 3 advantages of stratification
Direct and logical, minimum assumptions need to be satisfied for appropriate analysis, and computational procedure is straightforward
What are 4 disadvantages of stratification
Small numbers of observations in some strata, many ways to form strata with continuous variables, hard to interpret when several confounders, and categorization can result in loss of information
What are advantages and disadvantages of multivariate techniques
+: Allows for simultaneous adjustment of several confounding variables in a single analysis
-: Needs more advanced training in statistics
