NBME 6 biostats

[firstaid2012]

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7. an investigator is evaluating the outcome of coronary artery bypass grafting conducted by two surgeons i the community in the past year. surgeon x who ooperates exclusively at a tertiary care facility, has a 30 day operative mortality of 3% surgeon y , who operates exclusively at a community care facility has a 30 day operative mortality of 1% . the difference n operative mortality between surgeon x and surgeon y is significant(p=0.05) the investigator concludes that patients should have care at the community care facility. which of the ff raises the most concern regarding the validility of this conclusion.
a. lack of control of case complexity
b. lack of control of patient cholesterol data
c. lack of control of patient follow up
d. lack of control of patient recuperation
e. unequal sample sizes between surgeons.


please explain

 

[thehundredthone]

Off of the top of my head, the difference in case complexity is the confounding factor. A tertiary care centre typically has a larger share of more complex cases that have been referred there since they cannot be adequately managed at a community care facility.