Lecture 14: Analytic epidemiology

What is the primary purpose of descriptive epidemiology?

Descriptive epidemiology is used when little is known about the disease and relies on preexisting data to illustrate potential associations.

What type of questions does descriptive epidemiology aim to answer?

Descriptive epidemiology addresses "Who, where, and when" regarding the disease.

What is the primary purpose of analytical epidemiology?

Analytical epidemiology is used when there is insight into various aspects of the disease and relies on the development of new data to evaluate causality of associations.

What type of question does analytical epidemiology aim to answer?

Analytical epidemiology addresses the question "Why" regarding the disease.

How does descriptive epidemiology differ from analytical epidemiology in terms of data sources?

Descriptive epidemiology relies on preexisting data, whereas analytical epidemiology develops new data.

What does descriptive epidemiology illustrate, and how does it contribute to disease understanding?

It illustrates potential associations and provides a foundation for further investigation into the disease.

How does analytical epidemiology contribute to understanding disease causality?

Analytical epidemiology evaluates the causality of associations by using newly developed data.

What is a hypothesis?

A hypothesis is an educated guess or an unproven idea, based on observation or reasoning, that can be systematically confirmed or refuted through investigation

How is a hypothesis typically expressed in statistical hypothesis testing?

A hypothesis is usually expressed as the "null hypothesis."

What is the null hypothesis?

The null hypothesis assumes there is no association between exposure and outcome, even if there is a suspicion that one exists.

Provide an example of a null hypothesis related to epidemiology.

There is no association between living in the Phoenix area and the incidence of coccidioidomycosis (Valley Fever) in dogs or people.

Provide another example of a null hypothesis in veterinary science.

There is no difference in the prevalence of internal parasites in pet dogs compared to those in shelters or pounds.

Why is hypothesis generation important in statistical testing?

It provides a testable conjecture that can be systematically confirmed or refuted to investigate relationships between variables.

What is the primary purpose of an analytic study?

The primary purpose of an analytic study is to test the null hypothesis and either reject it or find it acceptable.

What is a key characteristic of a well-designed study?

A well-designed study isolates the many variables that can affect the outcome and excludes those outside the design of the study.

How do observational studies differ from experimental studies in terms of variable control?

Observational studies often involve less control over variables, while experimental studies are designed to isolate and control variables to test specific hypotheses.

Why is controlling variables important in an analytic study?

Controlling variables ensures that the results of the study are due to the factors being investigated and not confounded by external influences.

How does an analytic study relate to the null hypothesis?

An analytic study is structured to systematically evaluate and test the null hypothesis, determining whether it should be rejected or accepted based on the data collected.

What is an observational study?

An observational study is one in which there is no intentional control of exposure; researchers observe and analyze data without intervention.

What defines an ecological study?

An ecological study analyzes populations or groups, not individuals, to evaluate interventions and outcomes.

Provide examples of ecological studies.

Incidence of diseases following vaccination programs.

Impact of tobacco taxes on tobacco use.

Hearing loss in certain occupations.

Study habits and grades among students.

What are advantages of ecological studies?

Provide insights into health contributors.

Can be conducted rapidly and at low cost.

Useful when individual-level data is unavailable.

What are disadvantages of ecological studies?

Imprecise exposure measurement.

Temporal ambiguity.

Prone to confounding and ecological fallacy.

What is a cohort study?

A cohort study observes a group sharing a common exposure over time to track outcomes.

What are the two main types of cohort studies?

1. Prospective cohort studies.

2. Retrospective cohort studies.

What is a prospective cohort study?

A study that follows subjects into the future to document new cases or outcomes (e.g., Framingham Heart Study).

What is a retrospective cohort study?

A study that uses historical data to determine exposure levels and outcomes that have already occurred (e.g., shipyard worker mortality study).

What is the measure of association in cohort studies?

The Relative Risk (RR).

What are advantages of prospective cohort studies?

Can assess multiple exposures.

Useful when hypotheses are vague.

Clearly defines exposures.

What are disadvantages of prospective cohort studies?

Not suitable for rare outcomes.

Time-consuming and expensive.

Risk of losing subjects during the study.

What are advantages of retrospective cohort studies?

Faster and less expensive.

Suitable for rare outcomes.

What are disadvantages of retrospective cohort studies?

Prone to bias (recall and historical data).

Unclear temporality.

What is a case-control study?

A study where subjects are defined by the presence (cases) or absence (controls) of an outcome, and their past exposures are compared.

What is the measure of association in case-control studies?

The Odds Ratio (OR).

What are advantages of case-control studies?

Effective for studying rare conditions.

Quick, inexpensive, and requires fewer subjects.

What are disadvantages of case-control studies?

Exposure measurement may be inaccurate.

Risk of selection, recall, and observer bias.

Cannot always prove causality.

What defines an experimental study?

An experimental study involves intentional control of exposure, such as assigning interventions to study groups and evaluating outcomes.

How are clinical studies conducted?

Subjects are randomly allocated to study groups (receiving the intervention) or control groups (placebo or no treatment).

What is the measure of association in randomized clinical trials?

The Relative Risk (RR).

What is a cross-over clinical trial?

A study where subjects switch groups midway, valuable for limited sample sizes but can lead to carry-over effects.

What are the types of blinding in clinical studies?

Single-blinded: Subjects do not know their group.

Double-blinded: Neither subjects nor investigators know the group assignments.

What are community studies?

Studies that aim to create educational or behavioral changes at a population level without randomization.

Provide examples of community studies.

Water fluoridation in communities.

Smoking cessation campaigns.

What is Relative Risk (RR)?

Relative Risk is the ratio of the incidence of an outcome in an exposed group to the incidence in an unexposed group, used in cohort studies and randomized clinical trials.

What is the formula for calculating Relative Risk (RR)?

RR= Incidence in exposed/Incidence in unexposed​​

[a/(a+b)]/[c/(c+d)]

Why can't Relative Risk (RR) be calculated in case-control studies?

Because the entire population at risk is not included or represented in case-control studies.

What is the Odds Ratio (OR)?

The Odds Ratio is the odds of exposure among cases divided by the odds of exposure among controls, most commonly used in case-control studies.

What is the formula for calculating the Odds Ratio (OR)?

OR=ad/bc

When are Odds Ratio (OR) and Relative Risk (RR) approximately the same?

For rare diseases, the OR and RR will be very nearly the same.

What does an RR or OR equal to 1 indicate?

Exposure has no association with the disease.

What does an RR or OR greater than 1 indicate?

Exposure may be positively associated with the disease.

What does an RR or OR less than 1 indicate?

Exposure may be negatively associated with the disease and may even be protective.

In which types of studies is Relative Risk (RR) used?

Cohort studies and randomized clinical trials.

In which type of study is the Odds Ratio (OR) most commonly used?

Case-control studies.

Why is the OR a useful measure in case-control studies?

It provides a rough estimate of Relative Risk when the true incidence in the population is unknown.

What is external validity?

External validity is the ability to generalize the results of a study to an external population.

What factors can affect external validity?

Use of a convenience sample (not random).

Random samples are more likely to demonstrate external validity.

What is internal validity?

Internal validity refers to the degree to which a study has used methodologically sound procedures, ensuring that observed differences are due to the treatment applied.

How can internal validity be maximized?

Randomization is the best method for maximizing internal validity and minimizing bias.

What is bias in epidemiological studies?

Bias is the systematic deviation of results or inferences from the truth.

What is the Hawthorne effect?

The Hawthorne effect occurs when participants change their behavior because they know they are being studied.

What is recall bias?

Recall bias occurs when cases remember an exposure more clearly than controls, leading to skewed data.

What is selection bias?

Selection bias happens when there is a systematic difference between the characteristics of those selected for the study and those not selected.

What is the Healthy Worker Effect (HWE)?

HWE is a type of selection bias where employed populations tend to have lower mortality rates than the general population.

What is observer bias?

Observer bias occurs when investigators, knowing the case or control status of participants, record exposures differently between groups.

What is confounding?

Confounding is the distortion of the effect of an exposure on an outcome due to the exposure's association with other factors that influence the outcome.

Provide an example of confounding.

Smoking is a confounder when studying the association between alcohol use and lung cancer, as smokers are more likely to drink alcohol and develop lung cancer.

How can bias and confounding be reduced in a study?

Randomization in population sampling or group assignment is the primary method for reducing bias and confounding.

What factors require a larger sample size in a study?

Heterogeneous populations.

Rare outcomes.

Lower tolerance for error.

What is the minimum sample size for non-probability sampling?

The minimum sample size is usually 30 subjects.

Why is a larger sample size generally preferred?

Larger sample sizes reduce sampling error and provide more reliable results.