Week 7: Infectious Disease Research & Study Designs and Measures of Association - Before and After Class Combined

Descriptive research

Research that describes the distribution, frequency, or patterns of a health condition or characteristic in a population.

Analytic research

Research that examines relationships between exposures and outcomes to investigate possible associations.

Observational study

A study in which researchers observe exposures and outcomes without assigning participants to an exposure or intervention.

Experimental study

A study in which researchers assign an intervention or exposure to evaluate its effects on an outcome.

Cross-sectional study

An observational study that measures exposure and outcome at approximately the same point in time.

Cohort study

A study that groups participants according to exposure status and follows them to compare outcomes.

Case-control study

An observational study that selects participants based on outcome status and compares their previous exposures.

Randomized controlled trial (RCT)

An experimental study in which participants are randomly assigned to intervention or comparison groups.

Exposure

A characteristic, behavior, treatment, or factor being investigated for its relationship with an outcome.

Outcome

The health event, disease, or condition that researchers measure or investigate.

Population

The larger group of people to whom researchers want the findings to apply.

Sample

The subset of a population that participates in a study.

Incidence

The occurrence of new cases of a disease or health outcome in a population over a specified period.

Incidence risk

The proportion of people initially at risk who develop a new outcome during a specified period.

Incidence risk formula

Number of new cases during the specified period divided by the number of people at risk at the beginning of the period.

Incidence rate

The frequency at which new outcomes occur relative to the total person-time at risk.

Incidence rate formula

Number of new cases divided by the total person-time at risk.

Prevalence

The proportion of a population that has a particular condition at a specified time or during a specified period, depending on the measure used.

Prevalence formula

Number of existing cases divided by the total number of people assessed.

New case

A case that develops during the specified observation period.

Existing case

A case that is already present when prevalence is measured.

Person-time

The total amount of time that all participants contribute while they remain at risk for the outcome.

Person-time denominator

The combined time contributed by participants while they are at risk.

Risk ratio (RR)

The risk of an outcome in one group divided by the risk in a reference group.

Risk ratio formula

Risk in Group A divided by risk in Group B.

Risk difference (RD)

The risk in one group minus the risk in the reference group.

Risk difference formula

Risk in Group A minus risk in Group B.

Rate ratio

The incidence rate in one group divided by the incidence rate in a reference group.

Rate ratio formula

Incidence rate in Group A divided by incidence rate in Group B.

Rate difference

The incidence rate in one group minus the incidence rate in a reference group.

Rate difference formula

Incidence rate in Group A minus incidence rate in Group B.

Prevalence ratio

The prevalence in one group divided by the prevalence in a reference group.

Prevalence ratio formula

Prevalence in Group A divided by prevalence in Group B.

Prevalence difference

The prevalence in one group minus the prevalence in a reference group.

Prevalence difference formula

Prevalence in Group A minus prevalence in Group B.

Odds ratio (OR)

A measure comparing the odds of exposure or outcome between two groups, commonly used in case-control studies.

Odds ratio formula for a 2 × 2 table

(ad)/(bc), where a, b, c, and d are the four cell counts in the table.

Odds

The probability that an event occurs divided by the probability that it does not occur.

Reference group

The comparison group used as the denominator for a ratio or the second group in a difference.

Ratio

One group's measure divided by another group's measure.

Difference

One group's measure minus another group's measure.

Null value for ratios

1; a ratio of 1 indicates equal measures in the two groups.

Null value for differences

0; a difference of 0 indicates no difference between the two groups.

Ratio of 2

The measure in Group A is twice the measure in Group B.

Ratio of 0.5

The measure in Group A is half the measure in Group B.

Positive risk difference

Group A has a higher risk than Group B when the difference is calculated as A minus B.

Negative risk difference

Group A has a lower risk than Group B when the difference is calculated as A minus B.

Percentage-point difference

The subtraction of two percentages; risk and prevalence differences are commonly expressed in percentage points.

Rate difference units

Events per unit of person-time, such as infections per 1,000 patient-days.

Cross-sectional study measure

Prevalence; prevalence ratios and prevalence differences can compare groups.

Cohort study measures

Incidence risk, incidence rate, risk ratio, risk difference, rate ratio, and rate difference, depending on the study design and data collected.

Randomized controlled trial measures

Incidence risk or incidence rate and corresponding measures of comparison, depending on the data collected.

Case-control study measure

Odds ratio, because participants are selected based on outcome status.

Association

A statistical relationship between an exposure and an outcome.

Causation

A relationship in which an exposure contributes to producing an outcome.

Confounding

When another factor related to both the exposure and outcome distorts the observed association.

Bias

Systematic error in the design, selection, measurement, or analysis of a study.

Random error

Variation caused by chance that can affect study estimates.

Selection bias

Error arising when the way participants are selected or retained systematically affects the results.

Information bias

Systematic error resulting from inaccurate or inconsistent measurement or classification of exposure or outcome.

Correlation

An observed relationship between variables that does not, by itself, establish that one causes the other.

Informed consent

A process through which participants receive relevant study information and voluntarily agree to participate.

Institutional Review Board (IRB)

A committee that reviews research involving human participants to help protect their rights and welfare when review is required.

Voluntary participation

Participation based on a person's choice, without coercion, with the ability to withdraw according to study conditions.

Confidentiality

Protecting participants' identifiable information from unauthorized disclosure.

Risk minimization

Reducing potential harm to participants as much as reasonably possible.

Fair participant selection

Choosing participants fairly rather than exploiting or unfairly excluding particular groups.

Parental permission

Permission from a parent or guardian for a minor to participate when required.

Child assent

A child's affirmative agreement to participate when assent is appropriate and required.

Cross-sectional antibiotic example

Among 100 exposed people, 10 cases gives 10% prevalence; among 400 unexposed people, 10 cases gives 2.5% prevalence.

Prevalence ratio in the antibiotic example

10% divided by 2.5% equals 4, meaning prevalence is four times as high in the exposed group.

Prevalence difference in the antibiotic example

10% minus 2.5% equals 7.5 percentage points.

Rate calculation example

30 infections divided by 2,000 exposed patient-days equals 15 infections per 1,000 patient-days.

Rate comparison example

20 infections divided by 4,000 unexposed patient-days equals 5 infections per 1,000 patient-days.

Rate ratio example

15 per 1,000 patient-days divided by 5 per 1,000 patient-days equals 3.

Rate difference example

15 minus 5 equals 10 additional infections per 1,000 patient-days in Group A compared with Group B.

What is the main purpose of descriptive research?

To describe the distribution, frequency, or patterns of a health condition or characteristic in a population.

What is the main purpose of analytic research?

To examine relationships between exposures and outcomes and investigate possible associations.

What distinguishes an observational study from an experimental study?

In an observational study, researchers observe exposures without assigning them; in an experimental study, researchers assign an intervention or exposure.

What is a cross-sectional study?

A study that measures exposure and outcome at approximately the same point in time.

What measure is commonly used in a cross-sectional study?

Prevalence, often compared between groups using prevalence ratios or prevalence differences.

How does a cohort study select participants?

Participants are grouped according to exposure status and followed to compare outcomes.

What measures can a cohort study calculate?

Incidence risk, incidence rate, risk ratio, risk difference, rate ratio, and rate difference, depending on the data.

How does a case-control study select participants?

Participants are selected based on whether they have the outcome, and their previous exposures are compared.

What measure is commonly used in a case-control study?

The odds ratio.

Why is the odds ratio commonly used in case-control studies?

Participants are selected based on outcome status, so the sampled numbers of cases and controls do not directly provide the population risk or incidence rate.

What is a randomized controlled trial?

An experimental study in which participants are randomly assigned to intervention or comparison groups.

What is an exposure in a research study?

The characteristic, behavior, treatment, or factor being investigated.

What is an outcome in a research study?

The health event, disease, or condition being measured.

What is incidence risk?

The proportion of people initially at risk who develop a new outcome during a specified period.

How do you calculate incidence risk?

Divide the number of new cases during the specified period by the number of people at risk at the beginning of the period.

What is incidence rate?

The frequency of new outcomes relative to the total person-time at risk.

How do you calculate incidence rate?

Divide the number of new cases by the total person-time at risk.

What is prevalence?

The proportion of a population that has a particular condition at the time or during the period being measured.

How do you calculate prevalence?

Divide the number of existing cases by the total number of people assessed.

What is the difference between incidence and prevalence?

Incidence measures new cases developing during a period; prevalence measures existing cases in the population at the time or period of assessment.

What is person-time?

The total time contributed by all participants while they remain at risk for the outcome.

Why is person-time useful?

It accounts for differences in how long participants are observed while at risk.

How do you calculate a risk ratio?

Divide the risk in Group A by the risk in Group B.

How do you interpret a risk ratio of 2?

The risk in Group A is twice the risk in Group B.