Epidemiology Quiz

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Questions and Answers

What is the primary focus of epidemiology as defined by MacMahon and Pugh?

The examination of healthcare systems and their effectiveness

The study of distribution and determinants of disease frequency in man (correct)

The analysis of genetic factors in specific populations

The study of environmental factors affecting health

In the context of the assessment, how many questions can a student get wrong and still achieve a perfect score?

1 question

2 questions (correct)

3 questions

4 questions

Which of the following formulations is NOT a calculation students should know?

Species distribution index (correct)

Attributable risk

Sensitivity and specificity

Incremental cost-effectiveness ratio

What type of questions involves applying learned information to choose the best response?

Application questions Signup and view all the answers

What term refers to the exposure method that might be used in intervention studies?

Population Signup and view all the answers

Which of the following topics has the least number of questions according to the breakdown provided?

Systematic reviews Signup and view all the answers

How many application questions are included in the assessment breakdown?

30 Signup and view all the answers

What is one of the key calculations in epidemiology that assesses the likelihood of a disease occurring within a specified time frame?

Prevalence rate Signup and view all the answers

What is the definition of incidence in a population?

The number of new cases of disease in a population over a specific period of time. Signup and view all the answers

Which of the following describes point prevalence?

The number of existing cases at one specific point in time. Signup and view all the answers

In the example of the nursing home residents, how many individuals were 'at risk' of developing diabetes?

750 residents Signup and view all the answers

What information is required to calculate the incidence proportion in a population?

Total new cases and population at risk over a certain period. Signup and view all the answers

How is the incidence proportion calculating in the given nursing home scenario?

25 cases divided by 750 residents at risk. Signup and view all the answers

What is the definition of person-time in a study?

The amount of follow-up time each participant contributes Signup and view all the answers

What does computation of person-time start with?

The day a person enters the study Signup and view all the answers

If the incidence density in a study was shown as 0.09 per person-year, how is it expressed in cases per 100 person-years?

9 cases per 100 P-Ys Signup and view all the answers

How is the incidence density ratio (IDR) calculated?

By dividing the incidence density of exposed by the incidence density of unexposed Signup and view all the answers

What is attributable risk a measure of?

The excess incidence due to exposure Signup and view all the answers

What was the risk of CHD in smokers according to the information provided?

28 per 1,000 Signup and view all the answers

In the example of smoking and CHD, what was the risk of CHD in nonsmokers?

17.4 per 1,000 Signup and view all the answers

What does a higher incidence density indicate in the context of exposed individuals?

Higher risk associated with exposure Signup and view all the answers

What is the main concern regarding inclusion criteria in testing?

Bias may be introduced through the testing performance. Signup and view all the answers

Which type of information bias involves the memory of participants?

Recall bias Signup and view all the answers

What is a key characteristic of differential misclassification?

It leads to different measurement accuracy for exposed and unexposed subjects. Signup and view all the answers

What is one consequence of random error in a study?

Can be reduced by increasing sample size. Signup and view all the answers

In the context of information bias, which scenario exemplifies interviewer bias?

Different interviewers prompt participants differently. Signup and view all the answers

Which type of bias occurs when different accuracy is introduced in data collection?

Differential misclassification Signup and view all the answers

What is the impact of systematic error on research estimates?

It reduces the accuracy of estimates, regardless of sample size. Signup and view all the answers

Which outcome measurement method was used to assess neurocognitive impairment in the referenced study?

Purdue Pegboard and MOART reaction time tests Signup and view all the answers

What is a primary limitation of the data in case-control studies regarding the generalizability of findings?

Selection bias may affect the sample population. Signup and view all the answers

In a case-control study, which of the following groups does 'cases' refer to?

Individuals who have the specific outcome being studied. Signup and view all the answers

Which of the following exposures could be investigated in a case-control study related to heart disease?

Genetic predisposition of the participants. Signup and view all the answers

What does the relationship between exposure and outcome signify in epidemiological studies?

Exposure may lead to a specific health outcome. Signup and view all the answers

What is a significant challenge when determining the effects of exposure in case-control studies?

It's unclear what would happen without the exposure. Signup and view all the answers

In case-control studies, what hypothesis is primarily tested?

Whether an exposure is associated with a disease. Signup and view all the answers

Which statement best describes the selection bias found in studies regarding COVID-19 mortality and treatment outcomes?

Researchers likely selected cases to suit their hypothesis. Signup and view all the answers

Which outcome is commonly associated with exposure in epidemiological studies?

Development of chronic diseases. Signup and view all the answers

What does the mortality rate represent?

The total number of deaths in a population over a period Signup and view all the answers

How is the case fatality rate calculated?

Number of deaths from a disease divided by total cases of the disease Signup and view all the answers

What was the case fatality rate of COVID-19 in Canada as of September 12, 2023?

1.14% Signup and view all the answers

What is proportionate mortality?

Percentage of deaths from a specific cause in a population Signup and view all the answers

What is one strength of case reports?

They identify unusual findings Signup and view all the answers

What is a key limitation of case series?

They may not be generalizable to the larger population Signup and view all the answers

What aspect of observational studies makes them similar to natural experiments?

They observe natural variation without manipulation Signup and view all the answers

Which of the following statements about stroke mortality is true?

It can calculate proportionate mortality relative to total mortality Signup and view all the answers

What common characteristic do case series and case reports share?

Both detail individual patient information Signup and view all the answers

What factor influences the validity of findings in a retrospective case series?

Dependence on existing records and data Signup and view all the answers

Study Notes

Exam Information

Exam will be held in Togo Salmon Hall, Room 130
72 multiple choice questions, including 2 bonus questions
Exam duration: 2 hours and 30 minutes
The denominator for scoring is 70, meaning students can miss 2 questions and still score 100%
30 application questions
29 definition questions
13 calculation questions

Question Types

Application questions: Utilize learned course material to select the best answer from provided options (e.g., classifying bias, identifying study designs)
Definition questions: Identify the correct definition of a concept, formula or study design
Calculation questions: Solve mathematical problems using appropriate formulas

Topics to Study

HTA: 11 questions
Bias: 8 questions
Genetic epidemiology: 7 questions
Causal inference: 6 questions
Observational studies: 6 questions
Health Measures: 5 questions
Nutritional epidemiology: 5 questions
Screening: 5 questions
Indigenous Cultural Safety: 4 questions
Confounding/EM: 2 questions
DTA: 2 questions
Fundamentals: 2 questions
ID Epi: 2 questions
RCT: 2 questions
Systematic reviews: 2 questions
Metabolomic epidemiology: 1 question

Calculations to Know

Incidence and prevalence
Case fatality rate
Proportionate mortality
Sensitivity and specificity
Incremental cost-effectiveness ratio
Direct and indirect vaccine efficacy
Attributable risk

Epidemiology Definition

The study of the distribution and determinants of disease frequency in humans, with applications to control health problems
The study of the distribution and determinants of health-related states and events in populations

Question Types (PICOT)

Population
Intervention
Comparator
Outcome
Time
Setting

Exposure

Population
Exposure
Comparator
Outcome
Time
Setting

Incidence

The number of affected people in a population at a specified time divided by the total number of people in the population at that point
Point prevalence (one point in time)
Period prevalence (over a period of time) —Number of new cases of disease in a population during a certain time period divided by the number of people at risk in the same population and time period

Incidence Proportion Example

Estimate the incidence proportion of Type 2 diabetes in a nursing home with 800 residents from Jan 1st 2022 to Dec 31st 2022; 50 residents already have diabetes
750 residents are at risk of developing over the 12 months (800-50)
25 residents develop diabetes over the 12-month period
Incidence proportion: 25/750 = 3.3%

Quantifying Death

Mortality rate: The number of deaths during a specific time period in a particular population
Proportionate mortality: The percentage of deaths in a population during a period of time from a specific cause
Case fatality rate: Percentage of people who developed a certain disease who died from it

Case Fatality Rate Example

As of Sept 12, 2023, Canada reported 4,716,000 cases of COVID-19
As of Sept 12, 2023, Canada reported 53,541 deaths from COVID-19
Canadian COVID-19 case fatality rate: 53,541/4,716,000 = 1.14%

Proportionate Mortality Example

Total mortality in 2016: 740/100,000 people/year
Stroke mortality in 2016: 39.2/100,000 people/year
Proportionate mortality from stroke: 39.2 / 740 x 100 = 5.3%

Observational Study Designs

Observational studies, also called 'natural experiments' where investigators don't manipulate treatments or exposures to observe natural variations.

Case Reports

Contain information about one person (patient)
Describe unusual symptoms or syndromes observed in the patient, potentially speculating on exposures.
Strengths: Identify unusual findings, describe the course in the hospital.
Limitations: Cases may not be generalizable, not systematic, causes or associations may have other explanations, and a case may be a rare form of illness.

Case Series

A group of case reports involving patients with a specific presentation who received similar treatment.
Contain detailed information about individual patients (Demographics, diagnosis, treatment, response and follow-up after treatment).
Defined protocol and inclusion/exclusion criteria.
Strengths: Similar to cases reports but with more people, can help identify rare conditions/characteristics.
Limitations: Retrospective data, depending on availability and accuracy, may be subject to selection bias, findings may not be generalizable, often impossible to know what would have happened to the cases if they had not been treated.

Relationship Between Exposure and Outcome

Exposure: Something an individual does, is, or is exposed to (e.g., Exercise, ethnicity, genetics, ingested substances).
Outcome: Something that happens to an individual (e.g., Diagnosis of a disease, an event, or fracture ).

Case-Control Study

Study design comparing individuals with an outcome (cases) to those without that outcome (controls) to evaluate potential exposures.
Example: Comparing individuals with a heart attack to those without, comparing caffeine use.

Measures of Association

Used in case-control studies to evaluate whether an exposure is associated with a disease.

Risk

In epidemiology, risk is the probability that an event will occur in the future (the occurrence of a disease)
Risk = (D+)/(D+ + D-) Where: D+ = number of cases with a particular disease D- = number of individuals without a particular disease

Odds

Odds is the ratio of probability an event will happen to probability it will not happen
Odds = (D+) / (D-) Where: D+ = number of cases with a particular disease D- = number of individuals without a particular disease

Calculating Risk in Case-Control

Since in a case-control study, events have already happened, "risk" (future probability) cannot be estimated directly. —The measure of Odds can be used as an acceptable approximation.

Prospective Cohort Studies

Identify a population, track exposure to a specific risk factor. Measure the outcome, for instance myocardial infarction, over time.
Example: Tracking caffeine intake, in those who are not currently suffering from heart attacks, prospectively to see if there is a link.

Prospective - Follow Over Time

A longitudinal study where the investigator follows subjects concurrently through time.

Issue with Risk Ratio

Calculating risk ratio assumes that all participants are followed for an identical duration, but dropouts and various entry times affect this.

Person-Time

Correcting the problem of varying follow-up times in a study. Each person's contribution to the study is measured in person-time units.

Calculating Person-Time

Determine individually, how much time each person participated in the study.
Determine the cases of incidence within that time
The ratio of incidence to person-time, equals incidence density
Incidence density = [Number of cases] / [Total person-time].

Incidence Density Ratio

Calculate person-years separately for exposed and unexposed groups.
IDR = (Incidence Density for Exposed)/(Incidence Density for Unexposed)
Ratio of incidence density rates in exposed Vs unexposed populations.

Attributable Risk

Excess incidence of disease due to exposure, quantified by subtracting the incidence in unexposed people from the incidence in exposed people.
In a cohort study, identify the incidence in exposed people. Find the incidence in unexposed individuals. Subtracting the incidence in the unexposed from the incidence in the exposed determines attributable risk; a measure used to determine how the incidence rate in the exposed group differs from the incidence rate in the unexposed group

Attributable Risk (Smoking & CHD)

Risk of CHD in smokers = 0.028
Risk of CHD in nonsmokers = 0.0174
Risk in smokers = 28 per 1,000
Risk in nonsmokers = 17.4 per 1,000
Attributable Risk from smoking = (28-17.4)/1000= 10.6 cases per 1,000 smokers.
10.6 cases of CHD per 1,000 smokers could be attributed to smoking

Bias

Sources of error that provide alternative explanations for findings.

Bias Types

Types of bias discussed include selection bias, information bias and confounding.

Selection Bias

A bias introduced when subjects chosen, or retained in the study, differ from the target population in a way that affects the results of the study.

Selection Bias in Cohort Studies

Loss to follow-up
Healthy worker effect
Non-response bias
Inclusion criteria

Selection Bias in Case-Control Studies

Control selection
Self-selection
Differential surveillance
Differential diagnosis
Differential referral

Information Bias

A bias in the measurements of exposure, covariates, or outcomes which leads to a difference in quality of information between comparison groups

Information Bias in Cohort Studies

Recall bias
Interviewer bias
Reporting bias
Misclassification [Differential, non-differential]

Information Bias in Case-Control Studies

Recall bias
Interviewer bias
Reporting bias
Misclassification [Differential, non-differential]

Misclassification: Random Error vs Systematic Error

Random Error: Reduces precision of estimates. Can be reduced with increased sample size.
Systematic Error: Reduces validity/accuracy of estimates. Cannot be reduced by increasing sample size.

Differential Misclassification

Outcomes are measured differently in exposed Vs unexposed individuals e.g., individuals with higher BMIs receiving more sensitive tests for heart disease compared to individuals with lower BMIs.
Exposure is measured differently for diseased vs. non-diseased individuals, e.g., individuals with heart disease having height/weight measured by hospital scale compared to those without who self-reported at home.

Recall Bias

A type of information bias where the memory of exposure history is altered by the present health condition/situation; individuals with a disease are more likely to remember past exposures differently from those without.

Recall Bias in Nutrition Epidemiology

Common problem with food frequency questionnaires (FFQ)
People forget what they ate
Individuals with specific diseases (e.g., diabetes) may recall their diet differently
Social desirability bias: Underreporting of poor dietary habits or exaggeration of good dietary habits

Combing Recall Bias

Rely on hospital records, blind participants/personnel to the hypothesis, and use biomarkers.

Confounding

A variable that distorts the effect of an exposure on an outcome.
A confounder is correlated with the exposure and exerts a causal effect on the outcome, and thus potentially falsely producing a correlation that may not truly exist.

Effect Modification vs Confounding

Effect modification: A third variable that modifies the relationship between the exposure and the outcome (i.e., the effect is different in the presence Vs absence of the confounder). If the effect modifier has a relationship with the exposure and the outcome and may change the direction or strength of an association, it is essential to consider that.
Confounding: A third variable that distorts the association between the exposure and the outcome by being systematically associated with the exposure and the outcome (i.e., the effect does not exist or may falsely appear to exist). It is also important to consider confounders in research.

Mantel-Haenszel Estimator

Used to estimate the overall effect of an exposure on an outcome when there is a confounding variable (e.g., comparing the impact of red meat on the development of colon cancer in men versus women).

"Randomized" Controlled Trials (RCT)

Randomization ensures that the treatment and control groups are similar in all respects except for the variable being studied, minimizing bias.
Control group/Comparison group: group that is not exposed/receiving the intervention. ——This group's results are compared to the treatment group to estimate/identify whether the intervention had a causal effect.

What is "trial"?

A test of an unproven intervention or treatment in a specific period of time

Internal vs. External Validity

Internal validity: The study is conducted methodologically. Proper randomization, blinding, reduction of unplanned crossover, non-adherence, and correct analysis methods.
External validity: The study results are applicable to other people, settings, situations, and time periods.

Minimizing Blinding

Double-blind: Data collectors and data analysts are blinded to participant treatment assignments.
Triple-blind: Physicians/Hospital staff treating participants are also blinded.

N-of-1 Trial

A trial where a single patient receives an intervention and a placebo sequentially.
Randomly assigned sequences to evaluate the outcomes of the intervention in the particular patient.

Vaccine Efficacy

Direct Vaccine Efficacy (VE): Protection in those who received the vaccine.
Indirect Vaccine Efficacy: Protection in those who did not receive the vaccine, due to those receiving the vaccine.
Assessed through RCTs and observational studies.
Calculation: [1 - (Odds Ratio/Risk Ratio)] x 100%

Herd Immunity

Resistance of an entire population to a disease.
Protective effect on susceptible individuals when a large portion of the group is immune prevents the circulation of the disease by reducing the likelihood of contact between infected and susceptible individuals.

Systematic Reviews

Methods used to identify best available evidence from multiple research findings.
Uses explicit systematic methods to make decisions.

Metabolomics - Definition

Comprehensive analysis of small molecules (metabolites) in a sample.
Usually uses analytical technologies and bioinformatics.
Includes both endogenous (e.g., amino acids, nucleic acids) and exogenous/xenobiotic (e.g., drugs, toxins) metabolites.

Metabolomics - Aim

Understanding disease pathogenesis (Mechanism of disease)
Biomarker development and applications.

Metabolic Epidemiology

Comprehensive analysis of metabolites to understand disease mechanisms and identify biomarkers.

Metabolomic + Nutritional Epidemiology

Biomarkers: Not all chemicals respond to diet. serum calcium etc, not sensitive indicators, but some correlate over substantial periods of time (Vitamin C). Many are impacted by non-dietary factors(confounding). Difficult methods for assessing biomarkers of intake (blood/muscle/fat biopsies).

Genetic Epidemiology

Study of the role of genes and their interaction with environmental factors in the occurrence of disease in human populations.
Aims: Determine risks related to allelic variants, map the genome for diseases/susceptibilities. Use genetic information to estimate causal relationships.

Genetic Variations

Genetic variations encompass changes in DNA sequence including inversions, translocations, fusions, deletions, and duplications.

Genetic Information

Whole genome sequencing (WGS) — Gathers all genetic information, allows new variant identification, comprehensive but comprehensive/expensive.
Whole exome sequencing (WES) — Focuses on exome regions, identifies exonic mutations, less expensive/comprehensive than WGS.
Genotyping arrays — Identifies a limited number of genetic variants, cheapest but most limited/uncomprehensive.

Linkage Disequilibrium (LD)

Association between genetic variants (SNPs) due to nonrandom inheritance.
SNPs that tend to be inherited together within a given population. Measured by the coefficient between 0 (completely independent) and 1(fully linked).

Genetic Association Studies

Exposure variables: Genetic variations (e.g., inversions, translocations).
Study designs: Prospective cohorts, case-control, nested case-control, cross-sectional, and case cohorts.

Mendelian Randomization

A study design used to investigate causal relationships between exposures and outcomes by exploiting genetic variants as instrumental variables.
Inference based on genetic variants, as opposed to a typical clinical study —Advantages of using genetic variants: Robustness to unmeasured confounders and to reverse causal mechanisms. —Caveats or potential problems with using this study design: Relevance assumption, exclusion restriction, and independence.

Health Technology

Interventions for health promotion/prevention/diagnosis/treatment/rehabilitation, e.g., vaccine, CT scanner, pharmacotherapy.

Health Technology Assessment (HTA)

Systematic evaluation of health technologies to assess their properties and effects, and to aid decision making regarding the usage of health technologies.
Assess whether the technology has clinical advantage, budget impact, cost-effectiveness, and who benefits from it.

Types of Health Economic Evaluation (HEE)

Used to compare multiple health program/technology options.
Cost-minimization analysis (CMA): Used when options have equal outcomes, choosing the least expensive.
Cost-effectiveness analysis (CEA): Comparing costs against outcomes(e.g. life years gained), finding the most cost-effective solution.
Cost-utility analysis (CUA): Using quality-adjusted life years (QALYs), a weighting of both the quantity and quality of life.
Cost-benefit analysis (CBA): Expressing costs and benefits in monetary terms, focusing on the economic value of the health programs

Measures used in Health Economics

QALYs: Quality adjusted life years, a composite measure combining both the quantity and quality of life.

Standard Gamble

Evaluates how individuals trade off risk against loss in health/outcomes.

Time Trade-Off

Evaluates patient preferences and choices for a reduction In time and overall quality of life/health outcomes.

Cost Benefit Analysis

Method of comparing costs with monetary results.

How to Order Programs by Health Gain

Using QALY gained.

Incremental Ratios

Used to asses the relative costs and benefits of two or more interventions.

Cost-Effectiveness Plane (CEP)

Graphical representation of cost-effectiveness ratios (ICERs) of multiple interventions, identifying which has the most favorable cost-to-effect ratio

Positionality

Analyzing one's own social position in relation to researched population; how social position, including privilege,shapes research processes, challenges institutional power, and recognize relationship with land and place.

Ownership, Control, Access, Possession (OCAP)

Indigenous principles guiding the collection, protection, use, and sharing of Indigenous data and information.

Challenges To Research

Lack of access to traditional lands
Health disparities
Economic instability and poverty
Racism

Collaborate With Community

Collaborative approach to research/project
Value indigenous knowledge.
Treat community members as equals. View the world through their perspective.
Apply the Two-Eyed Seeing Approach; using Indigenous and Western knowledge.
Make research useful to the community.
Reciprocating benefits.

Certainty (Quality) of Evidence

Using GRADE approach
Five domains can downgrade the certainty, and three domains can upgrade.

Bradford Hill Criteria

Guidance for establishing causations amongst factors and disease patterns.
Multiple criteria/criteria should be used.

Live Birth Bias

Also known as "selective survival bias."
Occurs in studies that only include live births from pregnancies.
Misses important information about outcomes of non-live births or miscarriages which can lead to potentially invalid or inaccurate assessments

Risk of Bias

Selective reporting of results, bias that arises due to the selective reporting of results (may occur due to the focus on findings that support a specific hypothesis)
Phenomenon that occurs across a research body of evidence but not within a single research study.

Target Trial

Hypothetical trial that addresses a causal question, applied to observational data.

Problem: Subjectivity in Analytic Decisions

Subjectivity in making decisions, including p-values, direction of effect, and magnitude of effect.

Sensitivity and Specificity

Sensitivity: Test ability to correctly identify individuals with a disease.
Specificity: Test ability to correctly identify individuals without a disease.
[Sensitivity and Specificity are components of a diagnostic test.]

Positive Predictive Value (PPV)

Probability that a positive test result indicates that a disease is present.

Negative Predictive Value (NPV)

Probability that a negative test result indicates that a disease is not present

Diet and Chronic Disease

Prospective cohort studies are the standard.
Large case-cohort, nested case-control studies have also been incorporated.
Large randomized trials for diet are very expensive and less common.

Total Energy Intake

Energy intake might play in an important role in health outcomes.
Between-person variation in energy intake might not reflect differences in nutrient composition.
Energy intake may be correlated with disease risk, not necessarily directly causal but likely influences risk

A Tale of 3 Bananas

Nutrient values vary with banana size and therefore, data interpretation should consider this fact when making assessments based on observations .

How Important is Misreporting?

Variability in the impact of misreporting on nutrients in foods with little content vs rich in nutrients .
Depends on hypothesis and exposure of interest.

WHO 10 Screening Criteria

Criteria for evaluating the usefulness of screening programs for specific health conditions.

Evaluation of Screening Programs

Lead time bias: Extra time between a diagnosis using screening and diagnosis based on clinical symptoms.

Primary Prevention

Focuses on preventing the disease from ever starting through individual, and community efforts/health support.
Activities occur before the development of the disease.

Secondary Prevention

Interventions focus on reducing the expression and severity of diseases that have already begun by identifying individuals early in the process.
Occurs between onset of disease and the development of symptoms.

Tertiary Prevention

Treatment and interventions aimed at managing long-term complex health conditions, improve quality and longevity of life, and reduce complications by slowing/blocking disease progression.

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Description

Test your knowledge of epidemiology concepts as defined by MacMahon and Pugh. The quiz covers key terms, calculations, and application questions related to disease occurrence and prevalence. Prepare to assess your understanding of critical epidemiological methods and definitions.