Section 4: Study Designs

Question 1

What are the 3 components of epidemiology?

Answer 1

1. Measure disease frequency
– Quantify disease
2. Assess distribution of disease
– Who is getting disease?
– Where is disease occurring?
– When is disease occurring?
--->Formulation of hypotheses concerning
causal and preventive factors
3. Identify determinants of disease

Question 2

What are the 2 types of primary studies?

Answer 2

1. Descriptive studies (describe occurrence of outcome)
2. Analytic studies (describe association between
   exposure and outcome)

Question 3

What is the big picture reason for an epidemiological study?

Answer 3

To prevent and control disease

Question 4

What are the types (designs) of descriptive studies?

Answer 4

1. case report
2. case series
3. descriptive epidemiology

Question 5

What are the types (designs) of analytic studies?

Answer 5

Observational Studies
1. ecologic study
2. cross-sectional study
3. case-control study
4. case-crossover study
5. cohort study
Experimental Studies
6. RCT (randomized controlled trials)
7. community trials

Question 6

What is a prospective study?

Answer 6

looks forward, looks to the future, examines future

events, follows a condition, concern or disease into the future

Question 7

What is a retrospective study?

Answer 7

looks back in time to study events that have already occurred

Question 8

What are case reports?

Answer 8

Detailed presentation of a single case or handful of cases. Generally report a new or unique finding
• e.g. previous undescribed disease
• e.g. unexpected link between diseases
• e.g. unexpected new therapeutic effect
• e.g. adverse events

Question 9

What is a case series?

Answer 9

analysis of the experience of a group of patients with a similar diagnosis

Question 10

What are the advantages of a case series?

Answer 10

• Useful for hypothesis generation
• Informative for very rare disease with few established risk factors
• Characterizes averages for disorder

Question 11

What are the disadvantages of a case series?

Answer 11

• Cannot study cause and effect relationships

* Cannot assess disease frequency

Question 12

What are cross-sectional studies?

Answer 12

exposures and disease status at a single point in time (a cross-section of the population)

Question 13

What are cross-sectional studies good for?

Answer 13

to study conditions that are relatively frequent with long duration of expression (nonfatal, chronic conditions)

Question 14

Do cross-sectional studies measure incidence or prevalence of disease?

Answer 14

prevalence

Question 15

What are cross-sectional studies not useful for studying?

Answer 15

rare or highly fatal diseases or a disease with short duration of expression

Question 16

What are the disadvantages of cross-sectional studies?

Answer 16

• Weakest observational design
• The temporal sequence of exposure and effect may be difficult or impossible to determine
• Usually don’t know when disease occurred
• Rare events and quickly emerging diseases a problem.

Question 17

What are case control studies?

Answer 17

an “observational” design comparing exposures in disease cases vs. healthy controls from same population; exposure data collected retrospectively

Question 18

What kind of study is best for when disease

outcomes are rare?

Answer 18

case control study

Question 19

What are the advantages of case control studies?

Answer 19

– Less expensive and time consuming

– Efficient for studying rare diseases

Question 20

What are the limitations of case control studies?

Answer 20

– Inappropriate when disease outcome for a specific
exposure is not known at start of study
– Exposure measurements taken after disease
occurrence
– Disease status can influence selection of subjects

Question 21

What are the strengths of a cohort study?

Answer 21

– Exposure status determined before disease detection
– Subjects selected before disease detection
– Can study several outcomes for each exposure

Question 22

What are the limitations of a cohort study?

Answer 22

– Expensive and time-consuming
– Inefficient for rare diseases or diseases with long latency
– Loss to follow-up

Question 23

What is a cohort study?

Answer 23

an “observational” design comparing individuals with a known risk factor or exposure with others without the risk factor or exposure; looking for a difference in the risk (incidence) of a disease over time

Question 24

What is the best observational design?

Answer 24

cohort study

Question 25

Is data in a cohort study usual prospective or retrospective?

Answer 25

prospective

Question 26

In an experimental study, what do you call the subjects in the study who actually receive the treatment of interest?

Answer 26

the treatment group

Question 27

In an experimental study, what do you call the subjects in the study who receive no treatment or a different treatment?

Answer 27

the comparison group

Question 28

What is a randomized control trial (RCT)?

Answer 28

a design with subjects randomly assigned to

“treatment” and “comparison” groups

Question 29

What type of study provides most convincing evidence of the relationship between exposure and effect?

Answer 29

a randomized control trial

Question 30

What is the “gold standard” of all research designs?

Answer 30

randomized control trials

Question 31

What are the disadvantages of randomized control trials?

Answer 31

–Very expensive
–Not appropriate to answer certain
types of questions (it may be unethical, for example, to
assign persons to certain treatment or comparison groups)