Other

Question 1

Define bias

Answer 1

• Systematic error in study resulting in incorrect estimate of association between exposure and disease
  
  • Unusual people participate
  • Exposure incorrectly measured
  • Outcome incorrectly classified

Question 2

What is selection bias

Answer 2

• Especially in case-control, occurs when cases and controls are selected related to the exposure status.
  
  • Example: hospital -based case-control study on relationship of OC use and thromboembolism. Because physicians were already aware of the possible relationship between the two, patients with the disease were more likely admitted if they were using OC

Question 3

Define an ecologic study

Answer 3

• Non-experimental study in which the unit of study is a whole population.
  
  • Study of group characteristics
  • Correlates frequency of disease with levels of exposure
  • Exposure data relating to a place are compared with health data collected on individuals but summarized by place
  • Often done in a cross-sectional manner. As a result, one doesn’t know what is cause and what is effect.
  • Scatter plots of populations are made correlating rates of disease with rates of exposure.

Question 4

What is an ecological fallacy?

Answer 4

• An association at the level of “populations” may not hold at the “individual” level.
  
  • The bigger the unit of aggregation, the greater the potential magnitude of the ecological fallacy

Question 5

What is the measure of association in an ecologic study

Answer 5

• Can estimate group-level prevalence