Module 4: Study Designs

Question 1

What is the healthy worker effect

Answer 1

Working population likely to more healthy than general population

Question 2

What is ecological fallacy

Answer 2

We can’t prescribe the characteristics of the group to the individuals within that group

Question 3

What is a transient exposure

Answer 3

An exposure that only lasts for a short time

Question 4

What study design would you use to demonstrate a causal association

Answer 4

Randomised control trial

Question 5

What is clinical equipoise

Answer 5

genuine uncertainty about benefit or harm of intervention

Question 6

What is descriptive epidemiology

Answer 6

The study of the distribution of health related states or events in specified populations. (person, place and time: observational)

Question 7

What is analytic epidemiology

Answer 7

The study of the determinants of health related states or events in specified populations. (associations: exposures and outcomes. Causation, observational or intervention studies)

Question 8

What are the descriptive study designs

Answer 8

Cross sectional and ecological

Question 9

What is a cross sectional study

Answer 9

Measures exposures and/or outcomes at one point in time

Question 10

What do cross sectional studies measure

Answer 10

Prevalence

Question 11

How is prevalence calculated

Answer 11

Number of people with disease at a given point of time / total number of people in the population at that point in time

Question 12

What is prevalence affected by

Answer 12

Incidence and duration

Question 13

What are cross sectional studies used for

Answer 13

Describe prevalence, compare prevalence (repeated CS studies: between groups or over time), to generate hypotheses, to plan

Question 14

Why is a lack of temporal sequencing a limitation

Answer 14

Exposure and outcome happened at the same time, cannot determine which caused the other

Question 15

What are the limitations of cross sectional studies

Answer 15

No temporal sequencing
Not good for rare outcomes and exposures.
Not good for assessing transient or variable exposures, findings dependent on when study is done. Measures prevalence not incidence

Question 16

What are the strengths of cross sectional studies

Answer 16

Assess multiple exposures and outcomes at the same time.
Quick, inexpensive
Generate hypotheses
Describe and compare prevalence, useful for planning

Question 17

What is the null value for odds ratios

Answer 17

1

Question 18

What is the null value for relative risk

Answer 18

1

Question 19

What is the null value for risk difference

Answer 19

0

Question 20

What are the analytical study designs

Answer 20

Cohort, case control, RCT

Question 21

What is the only interventional study

Answer 21

RCT

Question 22

What do ecological studies measure

Answer 22

Exposures and outcomes across groups. Every data point a population

Question 23

What do cohort studies measure

Answer 23

Individuals defined based on basis of presence or absence of an exposure and followed up to see if they develop the outcome

Question 24

What do case control studies measure

Answer 24

Ascertain outcome status of individuals and then find out their exposure. Measure exposure using density sampling.

Question 25

What do RCTs measure

Answer 25

Participants randomly allocated to groups. Always have a comparison (control) group. Testing effects of treatments/interventions

Question 26

What are the strengths of ecological studies

Answer 26

Data often routinely collected and readily available. Easy, inexpensive Ability to compare between populations Useful for considering hypotheses Good for population level exposures

Question 27

What are the strengths of cohort studies

Answer 27

Good for studying rare exposures, determine temporal sequence between exposure and outcome, can examine multiple outcomes

Question 28

What are the strengths of case control studies

Answer 28

Good for studying rare outcomes, transient exposures, can examine multiple exposures, temporal sequencing

Question 29

What are the strengths of RCTs

Answer 29

Best way to evaluate an intervention. Strongest design for demonstrating a causal association Best way of testing interventions

Question 30

What are the limitations of cross sectional studies

Answer 30

No temporal sequencing Not good for rare outcomes and exposures. Not good for assessing transient or variable exposures, findings dependent on when study is done. Measures prevalence not incidence

Question 31

What are the limitations of ecological studies

Answer 31

Ecological fallacy: can’t prescribe the characteristics of the group to individuals within that group. Cannot control for confounding, cannot show causation

Question 32

What are the limitations of cohort studies

Answer 32

Loss to follow up can cause bias. Potential for misclassification of exposures and/or outcomes. Not good for rare outcomes. Time consuming, potentially expensive, healthy worker effect may cause bias, potential for participants to have change in exposure. Use existing data that may have been collected for other reasons leading to questionable quality. May not know about all relevant factors, selection bias

Question 33

What are the limitations of case control studies

Answer 33

Usually can only study one outcome, difficult to select appropriate controls, susceptible to selection and recall bias

Question 34

What are the limitations of RCTs

Answer 34

Loss to follow up can cause bias. Blinding difficult to achieve and may be obvious or cause safety issues. Non adherence can cause bias, ethical issue of harmful or less effective interventions- need clinical equipoise. Resource intensive, exposure need to be modifiable, highly selective which can hinder generalisability, so doesn’t reflect real world.

Question 35

Which two studies use prevalence as their measure of occurrence

Answer 35

Cross sectional and ecological

Question 36

Which two studies use incidence as their measure of occurrence

Answer 36

Cohort, RCT

Question 37

Which study has no measure of occurrence

Answer 37

Case control

Question 38

Case control vs cohort

Answer 38

Case control: known outcome, looking for exposure Cohort: known exposure, looking for outcome

Question 39

Which two studies have no measure of association

Answer 39

Cross sectional and ecological

Question 40

Which 2 studies use relative risk as their measure of association

Answer 40

Cohort and RCTs

Question 41

Which study uses odds ratio as its measure of association

Answer 41

Case control