A group of individuals with at least one common characteristic.
Term
What is a fixed population?
Definition
A population whose membership is defined on he basis of some event that happens once; permanent.
Term
What is a dynamic population?
Definition
A population whose membership is defined by being in a state or condition; transient.
Term
What is a population sample?
Definition
A selection, subgroup, of people that is representative of the source population.
Term
Why do we sample a source population?
Definition
More cost and time efficient, addresses limited resources. Well-designed sample study can provide same results as source population study.
Term
What is a health outcome?
Definition
Any measurable disease, disability, injury, infection, syndrome, symptom, biological marker, or positive health state.
Term
What is an exposure?
Definition
Any measurable characteristic that differs across individuals and affects or is associated with health. Biologic, chemical, or physical.
Term
What is the difference between a summary parameter and statistic?
Definition
A parameter describes population N, a statistic describes sample size n.
Term
Describe the 4 variables utilized in this course.
Definition
Dichotomous-2 possible values Ordinal-More than 2 ranked responses Categorical-More than 2 non-ranked and unordered responses Continuous-Assumes any value between minimum and maximum
Term
What is a mean?
Definition
Sum of all values, divided by total number of values in data set.
Term
What is a median?
Definition
Middle value in a set of observations, 50% of values above, 50% of values below.
Term
What is a sample quartile?
Definition
A ranked data set in which values are divided into four equal groups, each referred to as a "quartile."
Term
What is the intraquartile range? (IQR)
Definition
The IQR is the middle 50% of a data set, ranging from Q1 to Q3. In calculation Q3 - Q1.
Term
What does a right skewed distribution look like?
Definition
The median lies below the mean, a small trail of outliers above these values.
Term
What does a left skewed distribution look like?
Definition
The mean lies below the median, a small trail of outliers below these values.
Term
What do you use mean/standard deviation v. median/IQR?
Definition
Mean/SD should be used when the data is more symmetrical, indicating no outliers, and the mean=median.
Median/IQR should be used if the data is skewed, and the median does not equal the mean.
Term
Describe the conceptual model for environmental exposure-related disease.
Definition
Source > Media > Micro-enviro > Exposure > Absorbed Dose > Bio Effective Dose > Altered Structure/Function > Disease
Term
What is the difference between association and causation?
Definition
Association is a statistical relationship between two variables. Causation means that the exposure produces the effect.
Term
What are the 3 essential attributes of a cause?
Definition
1. Association: causal factor must occur together with effect, if X changes, Y changes. 2. Time order: cause must precede effect 3. Direction: asymmetrical relationship between cause and effect, C precedes E.
Term
Describe the Causal Pie model, and its sub-components: sufficient cause, component cause, necessary cause.
Definition
Sufficient: A minimal set of conditions and events that are sufficient to cause disease. Component: A single condition or event that acts within a sufficient cause. Necessary: A single condition or event that is required within each and every sufficient cause.
Term
What is causal inference?
Definition
The process of making conclusions about the causal connection between 2 variables. 1. Measure disease > 2. Verify results > 3. Assess causation. The assessment is best-judgment call using epi evidence.
The length of time during which an individual is exposed. Acute or chronic.
Term
What is an acute exposure?
Definition
An exposure that lasts for a relatively short period of time. Typically short-term contact with an agent or experience. May not repeat.
Term
What is a chronic exposure?
Definition
An exposure that is stable over a period of time, possible a lifetime.
Term
What is a constituent exposure?
Definition
A subset of chronic exposure, in which the exp doesn't change over the course of one's life. This exposure could be part of one's biological make-up such as race, ethnicity.
Term
What is a time-varying exposure?
Definition
An exposure that varies in intensity over the course of one's life.
Term
What is an occupational exposure?
Definition
On-the-job exposure.
Term
What is the relevance of exposure timing?
Definition
The period of time during which an individual is exposed. This consists of the critical window, or specific period of increased susceptibility to health effect. Latency describes the time from exposure to adverse health effect.
+ easy, inexpensive, collect data on any exp you want, feasible for large samples
- prone to errors, recall bias, differences between those that choose to respond v. those that ignore request to self-report
Term
What is an exposure assessment?
Definition
An applied science for measuring human contact with environmental contaminants. Consists of steps Source > Absorbed Dose in the conceptual model for Enviro Exp-related Dis.
Term
What is community monitoring?
Definition
Measuring an exposure in a community or region. Area-sampling is a subset.
Term
What is personal monitoring?
Definition
Measuring an exposure to a specific individual using a portable or personal sample device.
Term
+/- Community/Personal Monitoring
Definition
+ objective, quantitative, usually continuous
- expensive, time consuming, may not capture exp level for every subject-variability, personal monitoring not feasible for large samples
Term
What are biomarkers?
Definition
Measure exposure to a specific contaminant or biological surrogate for a contaminant IN THE BODY.
Term
+/- Biomarkers
Definition
+ objective, quantitative, accurate/precise data
- expensive, time consuming, exp at single point may not be relevant to the outcome, not feasible for large samples
Term
How do environmental hazards arise?
Definition
Transport: movement of contaminants within or between environmental media.
Fate: chemical or physical transformations and final destination of contaminants in the enviro.
Term
What is toxicology?
Definition
Study of adverse effects of chemicals or physical agents in living organisms, including their fate and transport in the body.
- high doses not relevant to humans, short exp time may not be relevant, interspecies extrapolation, ethics
Term
What is a dose?
Definition
Amount of environmental contaminant that is internalized into the body.
Term
Describe a dose-response curve.
Definition
A quantified relationship between dose and the effect, shows % response according to variation in dose. A threshold value may have NO response for small doses, and spark a response at a specified dose value.
Term
What is occupational health epidemiology?
Definition
The study of workplace exposures and associated health effects.
Term
Describe the hierarchy of controls for eliminating contact with hazard.
Definition
1. Elimination 2. Substitution-replace hazard 3. Engineering controls-isolate hazard 4. Admin controls-change the way people work 5. PPE-protect worker
Term
What are the steps to measure the frequency of disease in a population?
Definition
1. Source population 2. Cases of disease-num 3. Size of source pop-den 4. Time
Term
What are the 3 measures of disease frequency? What do they have in common?
Definition
Prevalence, cumulative incidence, incidence rate.
All are # cases/size of source pop, during specified time.
Term
What is prevalence?
Definition
The proportion of a population that has disease at a specified point in time. Existing, being in a state, total source pop, point in time.
Term
How do you calculate prevalence?
Definition
# existing cases at time point/# in total population at time point, NO UNITS, say time point
Term
What is incidence?
Definition
Measure occurrence of new cases. Involves transition of one state to another, source population AT RISK.
Term
How do you calculate cumulative incidence?
Definition
# new cases during time period/# total population at risk during time period, NO UNITS, include time period ASSUME: all people in source pop have been followed for ENTIRE specified period
Term
Interpret prevalence.
Definition
On the prevalence of in was <%>.
Term
Interpret cumulative incidence.
Definition
In , the
Term
How do you calculate incidence rate?
Definition
# new cases during time period/ total person-time of observation in pop at risk, UNITS person-time, state study time
Term
Interpret incidence rate.
Definition
The incidence rate of among was <#cases/PY> during
Term
+/- CI v. IR
Definition
CI easily calculated and understood, but assumes complete follow-up which is not typical. Appropriate for fixed population with minimal LTF.
IR takes into account when disease occurs, doesn't assume LTF, but is not intuitive to interpret and can be difficult to obtain. Appropriate for dynamic pops or substantial LTF.
Term
What are the criteria for epi hypotheses?
Definition
1. Compare 2 groups, exp and unexp 2. Predict direction of expected associated 3. Testable
Term
What is an absolute measure of association?
Definition
The difference between two disease frequency measurements. Prevalence Diff: Pexp-Pun (no units) Risk Diff: CIexp-CIun (no units) Rate Diff: IRexp-IRun (p-t units)
Term
Interpret risk difference.
Definition
The exposed had <#> of per compared to the unexposed over
Term
What is a relative measure of association?
Definition
Based on the ratio between 2 measures of disease frequency. Prev Ratio: Pexp/Pun (no units) CI/Risk Ratio: CIexp/CIun (no units) IR Ratio: IRexp/IRun (no units) Odds Ratio: ORexp/ORun (no units)
Term
Interpret risk ratio.
Definition
had <#> times the risk of developing over
Term
What is excess relative risk?
Definition
(RR-1)*100%
If RR=2.3... had 130% increased risk of developing compared to over
Term
Compare RR and RD.
Definition
RD is absolute, quantifies excess risk/rate of disease in exp v unexp groups, represents measure of PH impact of exp on dis occurrence
RR is relative and quantifies the relative risk/rate of dis in exp v unexp groups, represents the measure of strength or magnitude of association bw exp and disease
Term
What is the difference between descriptive and analytic epi?
Definition
Descriptive monitors public's health/planning, evaluates intervention programs, generates hypotheses. Identifies and counts disease in pop.
Analytic evaluates hypotheses, evaluates intervention programs, compares groups to systematically determine if there's an association.
Term
What is a case report/series?
Definition
A detailed report on ONE individual with a new or unusual health situation. Series: single group of individuals.
Term
+/- Case Reports/Series
Definition
+ quick, inexpensive, describe new health problems, generate hypos, insight into disease mechanisms
- no formal comparison group, cannot infer temp sequence
Term
What is a cross-sectional study?
Definition
A study that compares current exposure status to current disease status at a single point in time. PREVALENCE.
Term
What are limits of cross-sectional study?
Definition
Limit 1: Unknown temporal sequence Limit 2: Exposure associated with "causing" disease or duration of disease?
Term
+/- Cross-Sectional Studies
Definition
+ quick, inexpensive, available data, early stage of knowledge, public health planning, no ecological fallacy
- can't infer temporal, prevalent cases of long duration may bias results, can't control confounding
Term
What is an ecologic study?
Definition
A study that examines associations between exposures and disease mechanisms at population level.
Term
What is ecologic fallacy?
Definition
This occurs when variables associated at the pop level are no associated in individuals.
Term
+/- Ecologic Studies
Definition
+ quick, inexpensive, early stage of knowledge, wide range of exps, sometimes only pop level data known
- ecologic fallacy, no control for confounding
Term
What is an experimental study?
Definition
Investigator assigns individuals to 2/more groups, one receives treatment, one doesn't. Investigator follows groups over time for incidence.
Term
What is difference between prevention and clinical trials?
Definition
Prevention aimed to prevent high-risk/healthy individuals from getting disease. Clinical aims to treat or cure disease.
Term
What is informed consent?
Definition
People are recruited or volunteer for a study, and all eligible volunteers provide informed consent before agreeing to randomized treatment. (purpose, treatments, risks, randomization, ability to withdraw)
Term
What is randomization? What's its purpose?
Definition
Each study participant has the same probability of receiving treatment. This ensures that treatment is the only difference between study groups. Table 1 of epi studies should be even across groups.
Term
What is blinding?
Definition
Lack of knowledge regarding whether a study participant has been assigned to the treatment or comparison group.
Term
What is a placebo?
Definition
Inert substance with the purpose of matching as closely as possible the experience of the comparison with that of the treatment group.
Term
What is compliance?
Definition
Following the study protocol exactly as required throughout the course of the trial.
Term
+/- Experimental Studies
Definition
+ can minimize bias and confounding, RCTs optimal to detect statistically small to moderate but worthwhile effects
- ethics: equipoise must be met, acceptability, feasibility
Term
What is a cohort study?
Definition
A study in which people who are free of disease and differ according to exposure are followed over time for incidence of disease.
Term
What is the difference between prospective and retrospective cohort studies?
Definition
In prospective, the outcomes have not yet occurred when the study begins. In retrospective, the outcomes have already occurred by the start of the study. PRO is better for confounding, less prone to bias, expensive, time consuming, not efficient for long latency. RETRO may have inadequate exp data, more prone to bias, cheaper, faster, efficient for long latency.
Term
What is the difference between general and special cohorts?
Definition
General cohort formed on basis of a common exposure, can study effects of multiple exposures on 1 or more outcome. Special cohort formed on basis of rare exposure, can study effects of single exposure on 1 or more outcome.
Term
How do you select a comparison group?
Definition
People cannot be simultaneously exposed and unexposed. Epis must select different sets of people who are as similar as possible.
Term
What's the difference between internal, external and general pop comparisons?
Definition
Internal compares two groups of the same population. External compares two separate groups. General pop compares a greater population.
Term
+/- Cohort Studies
Definition
+ clear temporal sequence, can calculate RD and RR, few ethical concerns, good confounding, efficient for rare, evaluate exp on multiple outcomes
- need large numbers of subjects, expensive, time consuming, not efficient for rare, LTF
Term
What is a Case-Control study?
Definition
A study in which cases of disease are IDed, and then a sample of the pop that produced the cases is identified as controls. Exps are determined for individuals in each group, and the occurrence of disease is compared in the exp and unexp groups. Cases are statistically precious-enroll many!
Term
When is it desirable to conduct a Case-Control study?
Definition
1. Exp data are expensive or hard to obtain 2. Disease has long induction and/or latency 3. Rare disease 4. Little known about disease 5. Underlying pop is dynamic
Term
What is a control?
Definition
Controls are a sample of the source population that produced the cases.
Term
How do you select controls?
Definition
1. Controls must come from the same source population as the cases. 2. Controls must be selected independently from exposure. Fulfill the "Would Criterion"
Term
What is an odds ratio?
Definition
The ratio of events to non-events. Calculated in a Case-Control study...can't calculate an absolute measure of association because study is sampled. THe total population isn't enumerated.
OR= (Cexp/COexp)/(Cun/COun)
Term
+/- Case-Control Studies
Definition
+ clear temporal, few ethics, less expensive, efficient for rare, can evaluated effects of single exp on single outcome
- study single outcome, inefficient for rare, more opportunity for systematic bias, can't directly calculate risks
Term
What is generalizability?
Definition
Extent to which the results from a study can be generalized (or extended) to people who did not participate in the study.
Term
What is random error?
Definition
Errors that arise from chance that lead to an incorrect estimate of frequency or association.
Term
What is the difference between a point estimate and confidence interval?
Definition
A point estimate is the single best estimate of a pop parameter. A CI is a range of plausible values at a state level of certainty.
Term
What is hypothesis testing?
Definition
A framework of specifying 2 hypotheses (null/alt) and comparing the relative probabilities of obtaining the sample data under each of these hypotheses.
Term
What is the difference between the decision rule and the p-value approaches?
Definition
DR: specify null/alt, summarize sample data in test stat, set up DR (historic value), calc test stat, conclusion
P-V: specify null/alt, select/calc test stat, find p-v, conclusion
Term
What is a p-value?
Definition
The probability of observing our study result, or one more extreme, by chance alone if the null hypothesis is true.
Term
What can you conclude if p-value is greater than or less than 0.05.
Definition
Less or equal: small, low degree of null hypo compatibility, reject null, result unlikely due to chance, stat signif
Greater: large, high degree of compatibility with null, fail to reject null, result likely due to chance, not stat sig
Term
What can p-values not tell us?
Definition
Evaluate role of bias, confounding, imply causation, indicate if null is true, indicated strength/direction, ID range of possible values for measure, determine clinical relevance
Term
What is difference between 1-tailed v. 2-tailed t-tests?
Definition
1-tailed: specifies direction of association prior to analysis in alt, mu is less than or greater than the null mean
2-tailed: does not specify direction in alt hypothesis, just that there's a difference, mu does not equal null mu, more conservative
Term
What's the difference between Type I and Type II error?
Definition
Type 1: false +, reject null when null is actually true...minimized by using standard stat methods Type 2: false -, didn't reject null when it's actually false...minimized by large sample size
Term
Describe the 3 different types of t-tests used in this course.
Definition
1. 1-sample...compare mean from study to a historical mean. 2. 2 independent sample...compare means of 2 different groups. 3. Paired sample...compared means of same group under 2 conditions.
Term
What should an epi result include?
Definition
Measure of effect, measure of significance, measure of precision of estimate
