Epidemiology Essentials
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The word ______ comes from the Greek words epi, meaning “on” or “upon”, demos, meaning “people”, and logos, meaning “the study of”.

epidemiology

What is the definition of epidemiology according to MacMahon and Pugh?

The study of the distribution and determinants of disease frequency in man.

What is the definition of epidemiology according to Last?

The study of the distribution and determinants of health-related states and events in populations, and the applications of this study to control of health problems.

Which of the following elements contribute to the creation of an intervention question?

<p>Setting</p> Signup and view all the answers

Which of the following elements contribute to the creation of an exposure question?

<p>Outcome(s)</p> Signup and view all the answers

What is prevalence?

<p>The number of affected persons present in the population at a specified time divided by the number of persons in the population at that time</p> Signup and view all the answers

What is the incidence proportion for Type 2 diabetes in a nursing home with 800 residents, where 50 residents have diabetes on Jan 1, and 25 develop diabetes over the next 12 months?

<p>3.3%</p> Signup and view all the answers

What is the definition of mortality rate?

<p>The number of deaths occurring in a population during a particular period of time.</p> Signup and view all the answers

What is the definition of proportionate mortality?

<p>The percentage of deaths occurring in a population during a specific period of time from a specific cause.</p> Signup and view all the answers

What is the definition of case fatality rate?

<p>The percentage of people who contract a particular condition who die from it.</p> Signup and view all the answers

If Canada reports 4,716,000 cases of COVID-19 and 53,541 deaths from COVID-19 as of September 12, 2023, what is the case fatality rate of COVID-19 in Canada?

<p>1.14%</p> Signup and view all the answers

If the total mortality rate in 2016 is 740 per 100,000 people per year and stroke mortality is 39.2 per 100,000 people per year, what is the proportionate mortality from stroke?

<p>5.3%</p> Signup and view all the answers

Which of the following best describes a case report?

<p>A study that involves one individual.</p> Signup and view all the answers

Which of the following best describe a case series?

<p>A study that involves a smaller group of individuals.</p> Signup and view all the answers

Case-control studies are not considered observational studies.

<p>False</p> Signup and view all the answers

What is a common way to define risk in epidemiology?

<p>The probability that an event will happen in the future.</p> Signup and view all the answers

Odds in epidemiology are defined as the probability of an event occurring, divided by the probability of the event not occurring.

<p>True</p> Signup and view all the answers

It is possible to directly measure risk in case-control studies.

<p>False</p> Signup and view all the answers

What type of study offers a direct estimate of risk?

<p>Prospective cohort studies</p> Signup and view all the answers

Why is calculating a risk ratio problematic when dealing with cohort studies?

<p>Because calculations often assume individuals have been followed-up for the same amount of time and the whole study has been completed. This assumption might not be valid in practice.</p> Signup and view all the answers

What is person-time?

<p>A way of correcting for the problem [incidence density] by accounting for the different amounts of follow-up time that each person contributes to a study.</p> Signup and view all the answers

The computation of person-time ends on a certain date based on individual criteria. This includes the last day for which data is available, the day of diagnosis for the condition of study, or the last day of study.

<p>True</p> Signup and view all the answers

How is incidence density calculated?

<p>By dividing the number of cases by total person-years in the group.</p> Signup and view all the answers

If there are 4 cases of disease in a group, and the total person-years in the group are 46, what is the incidence density?

<p>0.09 cases per person-year, or 9 cases per 100 person-years.</p> Signup and view all the answers

What is the definition of attributable risk?

<p>The ``excess'' incidence due to exposure.</p> Signup and view all the answers

If the risk of CHD in smokers is 28 cases per 1,000 individuals, and the risk of CHD in non-smokers is 17.4 cases per 1,000 individuals, what is the attributable risk of CHD due to smoking?

<p>10.6 cases per 1,000 individuals.</p> Signup and view all the answers

The prevention of 10.6 cases of CHD per 1,000 smokers is possible if all smokers quit smoking.

<p>True</p> Signup and view all the answers

Which of the following are considered types of bias in research?

<p>Information Bias</p> Signup and view all the answers

Selection bias refers to an error that arises from participant selection in a study.

<p>True</p> Signup and view all the answers

Information bias in research may arise from errors in the measurement of exposure, covariates, or outcomes.

<p>True</p> Signup and view all the answers

Confounding variables can influence the study outcome.

<p>True</p> Signup and view all the answers

What are factors that can influence variable misclassification?

<p>Systematic error</p> Signup and view all the answers

Differential misclassification can occur when measurements of an outcome vary depending on the exposure status of the individuals.

<p>True</p> Signup and view all the answers

Recall bias suggests that individuals may have a distorted memory of exposure history due to their present health status.

<p>True</p> Signup and view all the answers

What are some techniques to combat recall bias?

<p>Using controls with a disease similar to the cases, utilizing hospital records, blinding study participants and personnel to the hypothesis, and employing biomarkers.</p> Signup and view all the answers

Confounding in research can occur when a third variable is associated with both the exposure and the outcome of interest but is not the focus of the study.

<p>True</p> Signup and view all the answers

Effect modification refers to a situation where the effect of exposure on the outcome varies depending on the level of a third factor.

<p>True</p> Signup and view all the answers

Which of the following are types of research design?

<p>Cross-sectional studies</p> Signup and view all the answers

Randomized controlled trials are designed to minimize bias by randomly assigning participants to either the treatment or control group.

<p>True</p> Signup and view all the answers

Blinding in research is a technique used to minimize bias by preventing participants or researchers from knowing the group assignment.

<p>True</p> Signup and view all the answers

An N-of-1 trial involves the sequential application of treatment and control interventions to a single individual to assess the effectiveness of the treatment.

<p>True</p> Signup and view all the answers

Direct vaccine efficacy refers to protection offered to individuals who have received the vaccine.

<p>True</p> Signup and view all the answers

Indirect vaccine efficacy refers to protection offered to individuals who have not received the vaccine due to the herd immunity effect.

<p>True</p> Signup and view all the answers

Vaccine efficacy can be assessed through only randomized controlled trials.

<p>False</p> Signup and view all the answers

Herd immunity suggests the resistance of a group to attack by a disease as a result of a large proportion of members being immune.

<p>True</p> Signup and view all the answers

What are systematic reviews?

<p>Systematic reviews are a type of research that identifies the best available evidence.</p> Signup and view all the answers

What is metabolomics?

<p>A comprehensive analysis of small molecules, both endogenous and exogenous, in a sample.</p> Signup and view all the answers

Small molecules in metabolomics include both endogenous metabolites and exogenous/xenobiotic compounds.

<p>True</p> Signup and view all the answers

What are the main goals of metabolomics research?

<p>Understanding disease pathogenesis and developing biomarkers.</p> Signup and view all the answers

Metabolomics studies can use existing correlations between data to make predictions.

<p>True</p> Signup and view all the answers

What are some limitations of biomarkers used to study nutritional intake?

<p>Not all chemicals reflect food intake over long periods of time.</p> Signup and view all the answers

The study of the role of genes and their interaction with environmental factors in the occurrence of disease in human populations is known as genetic Epidemiology.

<p>True</p> Signup and view all the answers

Genetic information can be used to estimate causal relationships between an exposure and a disease.

<p>True</p> Signup and view all the answers

There are various methods used to study genetic information.

<p>True</p> Signup and view all the answers

Linkage disequilibrium (LD) is a phenomenon that reflects a non-random association between two or more SNPs.

<p>True</p> Signup and view all the answers

Mendelian Randomization is a technique that utilizes genetic variants to study the causal relationship between an exposure and an outcome.

<p>True</p> Signup and view all the answers

What are the types of study designs used in genetic association studies?

<p>Case-cohort</p> Signup and view all the answers

Genetic variations are the basis for the development of various diseases.

<p>True</p> Signup and view all the answers

Study Notes

Epidemiology Calculations

  • Incidence and prevalence are key measures
  • Case fatality rate is the percentage of deaths from a specific cause
  • Proportionate mortality is the percentage of deaths from a specific cause in a population
  • Sensitivity and specificity measure test accuracy
  • Incremental cost-effectiveness ratio compares costs and benefits of interventions
  • Direct and indirect vaccine efficacy measure vaccine effectiveness
  • Attributable risk measures the risk of a disease due to exposure

Epidemiology Definition

  • Epidemiology studies the distribution and determinants of health-related states and events in populations
  • It applies this study to control health problems
  • The word "epidemiology" comes from Greek words meaning "on people" and "study of"

Intervention Questions

  • Questions related to interventions, etiologic studies, or diagnostic and screening studies
  • Key components are Population, Intervention, Comparator, Outcome(s), Time, and Setting

Exposure Questions

  • Questions related to interventions, etiologic studies, or diagnostic and screening studies
  • Key components are Population, Exposure, Comparator, Outcome(s), Time, and Setting

Incidence

  • Number of affected persons in a population at a specific time divided by the total population at that time
  • Point prevalence is calculated at one point in time
  • Period prevalence is calculated over a time period

Incidence Proportion Example

  • Example calculating incidence proportion of type 2 diabetes in a nursing home from January 1st to December 31st, 2022.

Quantifying Death

  • Mortality rate is the number of deaths in a population during a specific period
  • Proportionate mortality is the percentage of deaths due to a specific cause
  • Case fatality rate is the percentage of people who contract a condition and die from it

Case Fatality Rate Example

  • Example calculation of the case fatality rate of COVID-19 in Canada as of September 12, 2023.

Note: Various calculations for incidence proportion, case fatality rate examples are included in the document sections.

Proportionate Mortality Example

  • Example calculation of the proportionate mortality from stroke in 2016.

Observational Study Designs

  • Observational studies, often called natural experiments, don't manipulate treatments or exposure
  • Researchers observe, rather than manipulate, natural variation

Case Reports

  • Summaries of individual patients' unusual symptoms or syndromes
  • May include speculations about exposure

Case Reports Limitations

  • Not generalizable, not systematic
  • May be a "unique" case
  • Could have other explanations for cause

Case Series

  • Group of case reports with common presentation and treatment
  • Includes patient demographics, diagnosis, treatment, response, and follow-up
  • Includes defined protocol and inclusion/exclusion criteria

Case Series Strengths

  • Identifies characteristics of rare conditions or treatment courses

Case Series Limitations

  • Retrospective depends on data and records
  • Selection bias
  • May not be generalizable to a population

Relationship Between Exposure and Outcome

  • Relationships between specific exposures (activities, characteristics, or exposures) to outcomes
  • Includes doing, being, or ingesting

Case-Control Study

  • Study design where researchers compare people with an outcome (cases) to people without (controls)
  • Identifying exposures that may be linked to the outcome
  • Analyzing data to identify possible exposures

Case-Control Study Example

  • Possible example using heart attacks for cases and those without for controls to identify if caffeine exposure would be a factor

Measures of Association

  • Case-control studies test hypotheses to evaluate if an exposure is associated with a disease
  • Measures of association are used to evaluate if a positive or negative association exists

Risk

  • Probability of an event occurring in the future
  • Risk is calculated as (D +) / (D+ + D-)

Odds

  • Probability of an event occurring divided by the probability of an event not occurring
  • Odds = (D +) / (D-)

Risk in Case-Control

  • In case-control studies, you cannot measure incidence directly
  • Odds provide a measure of association from which incidence or risk can be calculated

Prospective Cohort Study

  • Study in which researcher follows a population to examine incidence or risk of an outcome
  • Subjects or cohorts are followed to see how they develop an outcome
  • Example provided of a prospective cohort study with caffeine and heart attack

Prospective - Follow Over Time

  • Longitudinal study to follow a population over time to examine population characteristics
  • Investigator observes subjects concurrently for time period

Issue with Risk Ratio

  • Calculation assumes everyone in study has been followed same amount of time
  • Drop-outs can cause issues since not all participants enter study at the same time

What is Person-Time?

  • Method for correcting incidence density calculations
  • Amount of follow-up time each person contributes to a study
  • Data calculation periods that begin when person is added to study and ends based on condition or end of study

Calculating Person-Time (Example)

  • Example of calculation (person-years) in a study

Person-Years

  • Incidence density is based on number of cases per person-year
  • Example provided for calculating incidence density
  • Example calculated incidence density

Incidence Density Ratio

  • Ratio of incidence density in exposed group to incidence density in unexposed group

Attributable Risk

  • "Excess" incidence due to exposure
  • Difference between risk in exposed and risk in unexposed
  • Example provided using smoking and heart disease

Bias

  • Sources of error that offer alternative findings explanations

Bias Types

  • Selection Bias
  • Information Bias
  • Confounding

Selection Bias (Cohort)

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

Selection Bias (Case-Control)

  • Control selection
  • Self-selection
  • Differential surveillance
  • Differential diagnosis
  • Differential referral
  • Non-response bias

Information Bias

  • Flaw measurements
  • Involves quality or accuracy of info
  • Example of cohort and case-control studies

Misclassification

  • Error in either exposure or outcome measurement
  • Random error reduces precision
  • Random error reduces precision of estimates

Differential Misclassification

  • Measurement of outcome different between exposed and unexposed
  • Example of BMI and heart tests
  • If measurement is different between diseased or non-diseased subjects

Note: Differential misclassification examples provided include varying methods of measuring outcome between exposed and unexposed groups, and between diseased and non-diseased groups.

Differential Misclassification Example

  • Exposure measurements different for diseased and non-diseased subjects, e.g height/weight difference between hospital-recorded and self-reported

Recall Bias

  • Memory of exposure history distorted by present health status
  • Examples in case-control studies

Recall Bias in Nutrition Epidemiology

  • Problems with FFQ (food frequency questionnaires)
  • Recall bias, social desirability bias
  • Underreporting of poor dietary habits
  • Exaggeration of good dietary habits (is a nondifferential misclassification)

Combatting Recall Bias

  • Use of hospital records
  • Study personnel blinded to hypothesis
  • Using biomarkers

Confounding

  • Variable that distorts exposure's effect, correlated to exposure and causes the outcome

Effect Modification vs Confounding

  • Sex example
  • Sex modifies drug effect

Mantel-Haenszel Estimator

  • Method for combining data from multiple studies or strata
  • Evaluates if crude OR is different from MH OR, or if they are equal but have stratified ORs that differ
  • Distinguishing confounder from effect modifier

Randomized Controlled Trials (RCT)

  • Randomization to establish similar groups
  • Only difference between groups is the intervention
  • Controlled group does not receive intervention

What is "Trial"?

  • Test of an intervention or treatment
  • Evaluation over a set period

Internal vs External Validity

  • Internal validity is when an RCT is conducted methodologically sound manner
  • Proper randomization, blinding, reduce unintended crossover, analysis correction
  • External validity is how generalizable findings are

Minimizing Blinding

  • Double-blind (data collectors, analysts)
  • Triple-blind (physicians, staff who treat study subjects)

N-of-1 Trial

  • Patient receives active and treatment creams in a randomly allocated sequence to study individual benefits

Vaccine Efficacy

  • Direct VE: Protection to those who received the vaccine
  • Indirect VE: Protection to those who did not receive the vaccine
  • Measures using RCT's and observational studies

Herd Immunity

  • Resistance of a population to an attack of a disease
  • Proportion of immune members lessening chance of susceptible individuals contacting the disease

Systematic Reviews

  • Identifies best available evidence, and systematically reviews existing research
  • Based on explicit methods and used to inform decision-making
  • Systematic use of research methodology

Metabolomics - Definition

  • Comprehensive analysis of metabolites
  • Using complementary technologies and bioinformatics
  • Metabolomics studies the biochemical processes. Metabolite molecules under <1500 Da

Metabolomics - Aim

  • Understanding disease pathogenesis and identifying biomarkers
  • Utilizing correlations & predictions between data

Metabolomics + Nutritional Epidemiology

  • Examine the relationship between diet and chronic disease
  • Identify if nutrients are affected by misreporting

Genetic Epidemiology

  • Role of genes in disease
  • Interaction between genes and environment
  • Risks determined from allelic variants on a disease

Genetic Variations

  • List different genetic variations
  • Inversions, translocations, duplications, insertions, etc.

Genetic Information

  • Whole genome and exome sequencing methods
  • Genotyping arrays

Linkage Disequilibrium

  • Genetic variants linked together and inherited together
  • Genetic variants not randomly assigned

Monogenic/Polygenic Phenotype

  • Single mutation resulting in altered phenotype (monogenic)
  • Multiple small changes genome-wide affecting phenotype (polygenic)

Mendelian Randomization

  • Using genetic variants as proxies for exposures,
  • Evaluate relationship between exposures and outcomes without confounding

Mendelian Randomization has 3 caveats

  • Relevance assumption (genetic variants associated with trait)
  • Exclusion restriction (variants only associated with trait not other traits)
  • Indpendence (no variables confounds/causes both)

What is "Health Technology"?

  • Any intervention for health promotion, disease prevention/diagnosis/treatment or rehabilitation/long-term care (e.g. vaccines, scans, etc)

What is "Health Technology Assessment (HTA)"?

  • Systematic evaluation of health technologies
  • Impacts, consequences, and consequences of health technology
  • Aiming to inform decisions

Cost-Effectiveness Analysis Types

  • Cost-Minimization Analysis (CMA)
  • Cost-Effectiveness Analysis (CEA)
  • Cost-Utility Analysis (CUA)
  • Cost-Benefit Analysis (CBA)

Cost-Effectiveness Analysis (CEA)

  • Method to determine what program/treatment achieves a given objective at the lowest cost
  • Consequences are expressed in non-monetary units

Cost-Utility Analysis(CUA)

  • Measure outcome (uses QALYs)
  • Combines measure of quantity and quality of life (QoL)

The Standard Gamble

  • Decision-making tool using options for varying outcomes, like health and lifespan.
  • Used to assess optimal healthcare choices (for example, with disabilities)

Cost-Benefit Analysis (CBA)

  • Evaluation comparing monetary costs to monetary benefits
  • Both assessed in terms of monetary values, like dollars

Ordering Interventions

  • Method ordering interventions from lowest to highest health gain (e.g. QALYs) by comparing cost to health outcomes

Incremental Ratios

  • Compares costs and effects of different interventions
  • Calculates differences in costs and effectiveness between interventions
  • Example: Implementing intervention C instead of A would cost $100 more per additional unit of benefit

Cost-Effectiveness Plane (Positionality)

  • Graphically represents cost-effectiveness of interventions

Ownership, Control, Access, Possession (OCAP)

  • Indigenous principles for data management
  • Indigenous people's ownership, control, access, and possession of data & info

Challenges to Research

  • Access to traditional lands
  • Health disparities and life expectancy
  • Economic instability and poverty
  • Racism

Collaborate With Community

  • Incorporate communities from the start
  • Treat community members as equals
  • Include communities' knowledge
  • Employ a Two-Eyed Approach

Certainty (Quality) of Evidence

  • GRADE approach to assess quality of evidence presented in research
  • Assess the certainty of evidence based on quality of studies and the presence of risk of bias issues

Bradford Hill Criteria

  • Method evaluating cause-and-effect relationship
  • Temporality, strength, dose-response, replicability, biological plausibility, consistence, specificity, considering alternate explanations

Lead Time Bias

  • Extra time between screening diagnosis and diagnosis based on symptoms
  • Seems to increase survival time after diagnosis, but is not a measure of actual survival time

Primary Prevention

  • Health actions before disease occurs
  • Reducing disease incidence by preventing disease from occurring

Secondary Prevention

  • Identifying asymptomatic individuals during a disease "window"
  • Treatment during window between start of disease and clinical symptoms
  • Improved survival

Tertiary Prevention

  • Treating or managing an existing condition
  • Slowing/blocking disease progression, reducing impairments and disabilities
  • Improving QoL

Sensitivity and Specificity

  • Sensitivity is the ability to correctly identify individuals with disease (numerator/denominator), and
  • Specificity is the ability to correctly identify individuals without disease (denominator).

Positive Predictive Value (PPV)

  • Probability test is positive when disease is present

Negative Predictive Value (NPV)

  • Probability test is negative when disease is absent

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