Measures of Association

Question 1

What are the two types of main studies in epidemiology?

Answer 1

Cohort and case-control study.

Question 2

Describe a cohort study.

Answer 2

A cohort study is comprised of persons with a common characteristic and typically has an exposed and unexposed cohort. A cohort is defined as any designated group of individuals who are followed or traced over a period of time.

Question 3

What is the purpose of a cohort study?

Answer 3

Purpose of cohort is to measure occurrence of one or more specific diseases during the period of follow-up usually with the aim of comparing disease rates for two or more cohorts.

Question 4

What is an experiment?

Answer 4

Experiment is a study in which incidence rate or risk of disease in two or more cohorts is compared after assigning the exposure to the people who comprise the cohorts.

Question 5

What is a clinical trial?

Answer 5

A clinical trial is an experiment that aims to evaluate incidence rates of disease complications in cohorts after assigning an intervention. Usually, this is done via an RCT. An RCT produces comparability between cohorts with respect to factors that might affect the rate of the disease complications.

Question 6

What is a field trial?

Answer 6

PPTs are not patients. The study is the primary prevention of a disease.

Question 7

What is a community intervention trial?

Answer 7

Exposure group is assigned to groups of people rather than single person.

Question 8

What is a standard requirement of a population at risk?

Answer 8

Everyone must be free of disease being measured at outset.

Question 9

What is the difference between a closed and an open cohort?

Answer 9

Open cohort will always take on new members.

Closed has fixed membership and will get smaller with time.

Question 10

What is induction time?

Answer 10

Time is takes for causal mechanism to be completed.

Question 11

What is a retrospective cohort study?

Answer 11

Identified from recorded information before beginning of study.

Question 12

What is a special-exposure cohort study?

Answer 12

Cohort studies that focus on people who share a particular exposure are called special-exposure cohort studies.

Question 13

What is a common exposure study?

Answer 13

Common exposure/general-population cohorts typically focus on exposure that a substantial proportion of the population have experience

Question 14

Describe a case-control study.

Answer 14

Two groups differing in outcomes are identified and compared on the basis of some supposed causal attribute.

To help determine if exposure associated with an outcome.

Control group is sampled from entire population that gives rise to the cases.

Calculate odds ratio.

Question 15

Define epidemiology.

Answer 15

Study of distribution and determinants (things that cause health outcomes) of health related states of events in specified populations and the application of this study for the control of health outcomes.

Question 16

What are the three Ds?

Answer 16

Disease
Determinants
Distribution

Question 17

Describe the three Ds.

Answer 17

Disease:
All possible results that may stem from exposure to a causal factor or intervention. Any health-related outcome (death, disease, disability, BH).

Determinants:
Any factor that brings about a change in health condition or other defining characteristic.

Distribution:
Refers to how disease of health states are found in a population.

Question 18

What is descriptive/surveillance data?

Answer 18

Monitor how much disease occurs in a population and compare measures across populations.

Question 19

Describe incidence.

Answer 19

New occurrences. Way of monitoring disease.

New cases during observation period/population at risk is CUMULATIVE INCIDENCE aka incidence proportion.

New cases/person-years is INCIDENCE RATE. Range 0 to infinity.

Question 20

Describe prevalence.

Answer 20

All existing cases of a disease.

People with disease at a point in time/total # of people in population at that time.

Between 0-1.

Is a proportion. Time must be specified.

Question 21

What is the difference between efficacy and effectiveness?

Answer 21

Efficacy is asking whether or not something works.

Effectiveness is the extent to which a treatment works in the real world.

Question 22

Describe nominal data.

Answer 22

Neither order nor magnitude are important. Data categorized.

Ex: eye colour

Question 23

Describe ordinal data.

Answer 23

Order is important, magnitude is not. Categorized. Intervals may not be equal.

Ex: Pain scale

Question 24

Describe discrete data.

Answer 24

Interval data is a type of discrete data. Order and magnitude are important. Intervals are equal. No true 0. Only whole numbers.

Question 25

Describe continuous data.

Answer 25

Can take on any value. Both order and magnitude are important.

Question 26

What is a count?

Answer 26

Number of event of persons with disease.

Question 27

What is a proportion?

Answer 27

Number of people with a disease/number of persons with and without disease.

Question 28

What are odds?

Answer 28

Probability/1-probability.

The odds that someone has the disease against odds that someone does not is the ratio.

Question 29

Give an example of going from odds to proportion and back.

Answer 29

•	Proportion and odds
o	20/100 = 0.20 is prop
o	Odds = 0.2/1-0.2 = 0.2/0.8=0.25
	1/0.2-1 is 4 so 1:4 odds
o	0.25/1+0.25 =0.20 (odds back to prop)

Question 30

Describe the relationships between odds and probabilities.

Answer 30

Probabilities between 0 and 0.5 = odds less than 1.

Probability of 0.5 = odds of 1.0.

Probability increase from 0.5 to 1.0, odds increase from 1.0 to infinity.

Question 31

Describe incidence proportion.

Answer 31

AKA cumulative incidence.

New disease/total number at risk. Time is specific. 0-1 range.

Question 32

Describe incidence rate.

Answer 32

New cases/total person time.
Time is baked into calculation.
0-infinity range.

Current risk better measured with this.

Question 33

Why measure prevalence?

Answer 33

Assess burden of disease.
Assess resource needs.
Estimate infectious population.
Allocate resources.

Question 34

What are the relative measures of association?

Answer 34

4 of them:

Prevalence ratio.
Risk ratio (incidence proportion).
Incidence rate ratio.
Odds ratio.

Question 35

Describe prevalence ratio.

Answer 35

Compare prevalence in one group to another.

Question 36

Describe risk ratio.

Answer 36

Compare cumulative incidence AKA incidence proportion in one group to another.

Question 37

Describe incidence rate ratio?

Answer 37

Compare incidence rate in one group to another.

Question 38

Describe odds ratio.

Answer 38

Compare odds ratio of exposed to odds ratio of unexposed.

Question 39

What is the difference between a positive association and a negative association?

Answer 39

Positive: exposure may cause disease.

Negative: exposure may be preventative.

Question 40

What are absolute measures of assocaition?

Answer 40

3 of them:

Prevalence difference
Risk difference
Incidence rate difference

Question 41

What is prevalence difference?

Answer 41

Difference in prevalence between exposed and unexposed within a population.

Question 42

What is risk difference.

Answer 42

Difference in cumulative incidence AKA incidence proportion between exposed and unexposed within a population.

Question 43

What is incidence rate difference?

Answer 43

Difference between incidence rate of exposed versus unexposed within a population.

Question 44

What is an absolute measure?

Answer 44

Measures how much an exposure counts for burden of disease between exposed and unexposed people within a population.
How much population level disease is prevented or added in presence of an exposure.

Question 45

What is a relative measure?

Answer 45

Measures how much as exposure counts for burden of disease between groups of exposed people (between populations).

Used to compare disease in one group to another.