Study Designs

Question 1

Define ‘experimental study’.

Answer 1

Used to study the effect of an intervention.

Question 2

Define ‘control group’.

Answer 2

Group that is given a placebo or an
alternative intervention.

Question 3

Define ‘experiment group’.

Answer 3

Group that is given the intervention being tested.

Question 4

Define ‘randomised control trial (RCT)’.

Answer 4

A study in which a number of similar people are randomly assigned to 2 (or more) groups to test a specific drug, treatment or other intervention.

Question 5

What is RCT useful for?

Answer 5

Studying causal effect of an intervention.

Question 6

Define ‘observational study’.

Answer 6

Observe the effect of a risk factor (or a treatment) without changing who is/isn’t exposed to it (unlike experimental
studies).
- Individuals are observed in a natural status

Question 7

Why is observational study less reliable than experimental study?

Answer 7

Causal inferences derived from observational studies are not as strong as those from experimental studies.

Question 8

Define ‘prospective study design’.

Answer 8

Researchers will follow and observe a group of subjects over a period of time to gather information and record the development of outcomes.

Question 9

List three features of prospective studies.

Answer 9

• Outcomes (even exposures) have not occurred when the study starts
• Sample includes people exposed or un-exposed to a risk factor
• Focus on the exposure groups

Question 10

Define ‘retrospective study design’.

Answer 10

Uses existing data that have been recorded for reasons other than research.

Question 11

List four features of retrospective studies.

Answer 11

• Outcomes of interest have already occurred when the study starts.
• Sample includes both cases & non-cases
• Focus on the outcome groups
• Data on exposures are from records or
  participants’ recall.

Question 12

Define ‘longitudinal study design’.

Answer 12

Researchers repeatedly examine the same individuals to detect any changes that might occur over a period of time.

Question 13

List three features of longitudinal studies.

Answer 13

• Data on both exposures & outcomes are collected repeatedly, at multiple time points.
• Can assess both between- and within-individual variations
• Can study changes of a measure with age

Question 14

Give two examples of longitudinal study.

Answer 14

• Height growth in childhood
• Decline of physical function over age

Question 15

Why is longitudinal study an important study design in life course research?

Answer 15

It’s suitable for studying temporal effect.

Question 16

Define ‘cross-sectional study design’.

Answer 16

The investigator measures the outcome and the exposures in the study participants at the same time.

Question 17

Why is cross-sectional study useful?

Answer 17

To study prevalence or inter-relationship
between measurements.

Question 18

Define ‘case-control study’.

Answer 18

Participants are selected for the study based on their outcome status. Thus, some participants have the outcome of interest (cases), whereas others do not have the outcome of interest (controls). The investigator then assesses the exposure in both these groups.

Question 19

What are the disadvantages of a case-control study?

Answer 19

• Exposures contain gaps
• Susceptible to bias
• Cases recall better on exposures than non-cases

Question 20

What are the advantages of a case-control study?

Answer 20

• Cost-effective
• Useful for rare diseases

Question 21

Define ‘prospective cohort study’.

Answer 21

Individuals which share some common characteristics are followed-up
to monitor potential risk factors and outcomes. Risk factors are measured before the outcomes have occurred.

Question 22

Define ‘retrospective cohort study’.

Answer 22

Identify diseased subjects by interview or written records.

Question 23

Define ‘historical cohort study’.

Answer 23

Individuals are traced years later
* Birth records were kept by hospitals (or researchers)
* Go back in time to identify a cohort, establish their exposure
status at the time.

Question 24

What are the advantages of historical cohorts?

Answer 24

• Useful when reliable records are available
• Less costly

Question 25

What are the disadvantages of historical cohorts?

Answer 25

• Often a huge gap in information
• Selection & misclassification bias due to retrospective nature.

Question 26

What are historical studies used for ?

Answer 26

Early fetal programming work.