Lecture: Stratified Case Control Study Design  


Assigned Reading

  1. Introduction to study design Read►
  2. Case control study design Read►
  3. Comparison of case control and cross sectional studies Read►
  4. Stratification matters Slides►
  5. Analysis of stratified data Slides►


For this assignment you can use any statistical package such as R or SAS.  You can also use SQL or Excel.  Work can be done in group's of two students but you cannot work with a student that you have previously teamed up with.

A. Calculate impact of physicians on complaint from the data in Table 1.  Redo Table 1 into two partial tables, where each partial table reports on complaints for the same nurse but different physicians.  In essence, use nurses to stratify impact of physicians on complaints.  Then calculate the Mantel-Haenszel test of association, test of homogeneity across strata, and the common odds ratio for impact of physicians on complaints. Explain if the common odds ratio can be used given the other two tests. 

B. In the following table calculate the marginal table that excludes the variable rehabilitation services.  Then calculate the impact of skilled nursing facility on above average cost, conditional on severity of illness and the surgeon involved.  To do so, create strata for the combination of severity of illness and surgeon and calculate the impact of skilled nursing facility on cost within each strata.  Redo, this time not conditional on surgeon involved.  What does this data tell you about impact of skilled nursing facility on the bundled cost.  Arpitha and Aryan's Responseâ–º

  N: Skilled Nursing Facility A Skilled Nursing Facility B
S: High Severity Low Severity High Severity Low Severity
O: Orthopedic Surgeon R: Rehab Services A: Above Avg Cost Below Avg Cost Above Avg Cost Below Avg Cost Above Avg Cost Below Avg Cost Above Avg Cost Below Avg Cost
Joe Yes 405 268 453 228 23 23 30 19
Joe No 13 218 28 201 2 19 1 18
Jim Yes 1 17 1 17 0 1 1 8
Jim No 1 117 1 133 0 12 0 17



For additional information (not part of the required reading), please see the following links:

  1. Criteria for reporting case control studies Read►
  2. Example of causal analysis of emergency room delays Read►

This page is part of the course on Comparative Effectiveness organized by Farrokh Alemi, PhD. Home► Email►