Potential Errors In Epidemiologic Studies. Bias . III. Dr. Sherine Shawky. Learning Objectives. Understand the concept of bias Recognize the methods to prevent bias Know the methods to evaluate the impact of bias. Performance Objectives. Prevent bias Evaluate bias Improve validity.
Dr. Sherine Shawky
Error due to systematic difference between the characteristics of the people selected for a study and those who are not.
Error due to systematic differences in the way data on exposure or outcome are obtained from various groups leading to misclassification of study subjects
Sources of data collection
Methods of data collection
Content of information
Increase Sample Size
When a survey is done and dichotomizes subjects according to exposure and outcome, validity of results can be analyzed by comparing the survey results to standard reference test in contingency table
Repeatability could be measured within observers (same observer on same subjects on different occasions) or between observers (different observers on same subjects) and results expressed in contingency table.
Identification of possible bias is a difficult exercise but is crucial to improve validity. Bias is most effectively dealt with through careful design and meticulous conduct of study. If potential source of bias is introduced, it is usually difficult to correct for its effect analytically.