Epidemiology: Analytic Study Designs

Question 0

Advantages of Cross-Sectional Studies

Answer 0

• Efficiency and Cost
• Generates hypotheses
• Generalizability of results: studies are based on a sample of the population, so the results may be generalized in reference to this population

Question 1

Process of Cross-Sectional Study

Answer 1

• Investigator selects a sample and measures both exposure and disease outcome at the same point in time for all subjects in the sample
• Includes individuals with prevalent rather than incidpent disease

Question 2

Cross-Sectional studies provide information about the

Answer 2

Frequency and characteristics of disease by providing a snapshot of the health experience of the population at a specified point in time.

Question 3

Disadvantages of cross-sectional studies

Answer 3

• Subject to temporal relationship problems: difficult to be certain the disease outcome could not have caused the exposure
• Subject to prevalence bias
• Subject to selection bias
• Subject to confounding
• Difficult to study rare exposures or rare diseases unless enrolling subjects according to these factors

Question 4

Process for cohort studies

Answer 4

Investigator begins with individuals without the outcome of interest. They are classified according to the presence or absence of exposure at baseline. Both exposed and unexposed individuals are followed for subsequent onset of the disease outcome

Question 5

Types of Cohort Studies

Answer 5

• Special exposure cohort

- General population cohort

Question 6

Special Exposure Cohort

Answer 6

• Subjects are selected to represent a specific exposure
• Used when exposure is unique or relatively rare
• Comparison groups may be drawn from the same population, from the general population, or from some other similar population

Question 7

General population cohort

Answer 7

• Sample is selected to represent a large segment of the population with a wide range of exposures
• Exposed groups and comparison groups are internal subgroups of the entire cohort being followed
• Preferred when the exposure of interest is relatively common and/or when there is interest in investigating more than one exposure simultaneously

Question 8

Prospective data collection

Answer 8

• Subjects are enrolled and exposure status is measured at a particular time, and the cohort is then followed forward into the future to ascertain development of disease

Question 9

Retrospective data collection

Answer 9

• Cohort is assembled based on past exposures from past records.
• Disease status is also assessed from past records or by contacting subjects in the present

Question 10

Sources of data for cohort studies

Answer 10

• Exposure information is taken at baseline and during the follow-up period
• Disease incidence is assessed over the follow-up period

Question 11

Advantages of cohort studies

Answer 11

• Time sequence
• Ethical to study etiological factors as well as treatments, since exposures were already there and not assigned by the investigator
• Rare exposures can be studied if a suitable exposed cohort can be identified
• Multiple outcomes can be investigated for a single exposure
• Less prone to selection bias because outcome is unknown at baseline and should not influence selection of participants
• Information bias less likely
• Incidence rates of disease can be measured

Question 12

Disadvantages of cohort studies

Answer 12

• Cost
• Usually not appropriate for rare disease outcome
• Validity: if not designed carefully, associations observed may not be valid
• Non-participation

Question 13

Process for case-control studies

Answer 13

Investigator finds subjects with the disease and subjects without the disease and then obtains data regarding past exposures from both groups

Question 14

Types of Case-Control Studies

Answer 14

• Population based

- Hospital based

Question 15

Population-based case-control studies

Answer 15

• Cases are a representative sample of call cases in a precisely defined and identified population and controls are sampled directly from the same population that gave rise to the cases

Question 16

Hospital-based case-control study

Answer 16

Cases are individuals with disease in specified hospitals or clinics.

Question 17

Assumptions of valid case-control study

Answer 17

• Cases and controls come from the same population

- Cases are representative of all cases from the area and controls are representative of all non-cases

Question 18

____ cannot be computed from case-control studies

Answer 18

• Incidence rates

- Must use odds ratio

Question 19

Advantages of case-control studies

Answer 19

• Rare diseases can be studied
• Multiple exposures can be investigated simultaneously
• Efficient
• Odds ratio is a good approximation of the relative risk estimated using incidence rates

Question 20

Disadvantages of case-control studies

Answer 20

• Validity may be compromised
  - Information bias
  - Selection bias
  - Prevalence bias
  - Confounding
  - Temporal relationship problems

Question 21

Nested case-control study

Answer 21

• A case control study nested in an ongoing cohort study
• Cases are members of the cohort who develop the disease of interest
• Controls are selected from other members of the cohort
• Exposures are based on information that was previously collected on all members of the cohort in a uniform fashion

Question 22

Process for intervention studies

Answer 22

• Investigator selects sample of willing subjects who are free of the disease from the target population, assigns an exposure to each subject, and then follows these subjects through time to monitor the occurrence of disease

Question 23

Types of intervention studies

Answer 23

• Clinical trails

- Field Trials

Question 24

Clinical Trials

Answer 24

• Therapeutic studies that are conducted among patients with disease
• Exposure is evaluated to determine whether it is effective in altering complications associated with disease

Question 25

Field Trials

Answer 25

• Primary preventions studies that involve healthy subjects or those at high risk of developing disease
• Exposure is evaluated to determine whether it is effective in reducing one’s risk of developing disease

Question 26

Advantages of intervention studies

Answer 26

• Only design that can truly prove causality
• Time sequence is controlled
• Selection bias is ruled out because inclusion of subjects into study is not based on exposure and disease status
• Multiple outcomes can be studied for a single exposure
• Incidence rates of disease among exposed and non-exposed can be measured directly

Question 27

Disadvantages of intervention studies

Answer 27

• Costs
• Feasibility: not all research questions are easily addressed
• Validity
  - Placebo effect
  - Information bias
  - Loss to follow-up and noncompliance
  - Confounding

Question 28

Study that assigns exposure and outcome is unknown

Answer 28

Intervention study

Question 29

Study that selects study groups based on exposure and outcome is unknown

Answer 29

Prospective cohort study

Question 30

Study that selects study groups based on exposure using past records, outcome is unknown

Answer 30

Retrospective cohort study

Question 31

Study that selects study groups based on outcome, exposure is unknown

Answer 31

Case-control study

Question 32

Study that finds single study group, exposure and outcome are both unknown

Answer 32

Cross-sectional study