Observational Studies 1

What is a case report?

Describe unusual symptoms or syndromes observed in one person. Generate hypotheses

What are advantages of case reports?

Highlight unusual and novel findings. Identify treatment side effects of drugs or treatment failures. Tetralogy.

What are limitations of case reports?

May not be generalizable. Not systematic. Causes or associations may have other explanations.

What is a case series?

A group or series of case reports involving patients with a specific presentation who were given similar treatment. Defined protocol and inclusion/exclusion criteria. Collect demographic information and clinical course.

What are advantages of a case series?

Quick and easy to conduct. Useful for hypothesis-generation. Detailed clinical information.

What are limitations of a case series?

No control group. Cases may not be representative. Other factors may influence outcomes. Descriptive.

What is a case-control study?

Select participants based on whether they have disease or not. Look backward for exposure.

How can you define a case in a case-control study?

Signs and symptoms. Physical and pathological examination. Diagnostic tests.

What are sources of cases in a case-control study?

Hospital or clinic patient rosters. Death certificates (e.g., Statistics Canada Death Database). Country surveys. Cancer registries (e.g., Canadian Cancer Registry).

When is a case-control study desirable?

Exposure data are difficult to obtain. The disease is rare. The disease has a long induction and latent period. Little is known about the disease. The underlying population is dynamic.

What should the controls of case-control studies be?

The “counterfactual” principle: The controls would have been cases, if they met the criteria. Source population.

What are sources of controls for case-control studies?

Sample from the general population. Individuals attending a hospital or clinic. Individuals who have died. Friends or relatives of the cases.

What are difficulties of population controls?

Time-consuming and expensive to identify. Low interest. Difficult for controls to recall past exposures.

What are considerations for hospital or clinic controls?

Reason for admission should not be linked to exposure of interest. Illness of the controls should have the same referral pattern as the cases.

What are the benefits of hospital or clinic controls?

Easy identification. Good participation rates. Recall of past exposures may be good.

When should deceased controls be used and what is the issue?

When some/all cases deceased when data collection began. Controls are not representative of source population.

What are benefits and disadvantages of friend/family controls?

Share case socioeconomic status, genetics, race, age, education. Case may not have friends/family; cases may not wish to reveal their illness to friends/family; controls will share some habits of cases.

What are the three methods for selecting controls?

Survivor sampling, case-base sampling, and risk-set sampling.

What is survivor sampling?

Controls are sampled from the source population at the end of the follow-up period.

What is case-base sampling?

Controls are sampled from the source population at the beginning of the study.

What is risk-set sampling?

Controls are sampled continuously over time as cases occur.

How to measure exposure history?

Questionnaires, pre-existing records, biomarkers.