A study investigated whether there was a higher risk of complications for a type
ID: 3218995 • Letter: A
Question
A study investigated whether there was a higher risk of complications for a type of colorectal surgery performed at a large urban hospital. University Hospital, versus a smaller regional hospital. County Hospital. 400 patients who had the surgery at County Hospital and 2.000 patients who had the surgery at University Hospital were studied. The following table summarizes the number of 'complications' in each group: Find the rate of complications in each group. Show your work below. County Hospital 3%. University Hospital 8%. Is this is an observational or an experimental study? Why? The data suggest that it is safer (in the sense of a lower rate of complications) to have surgery at County Hospital. Discuss whether this implies that a patient should consider having surgery at County Hospital in order to reduce the risk of complications. Identify at least one plausible confounding factor and one plausible mediating factor that could partly explain the results of the study. (Continue on the back of the page if necessary) How could you design a study to establish whether it is safer to have surgery at County Hospital than at University Hospital? What obstacles would you face? (Continue on the back of the page if necessary)Explanation / Answer
a)County hospital=12/400=3%,University Hospital=160/2000=8%.
b)Observational because subjects are not assigned to hospital by the experimental basis.
c)The choice of hospitals does not necessarily cause the change in risk because riskier cases may tend to be sent to University Hospital which may have the expertise and facilities to handle more serious cases.
Thus a plausible confounding factor would be preoperative risk which may influence the choice of hospital and affect the risk of complication.
Plausible mediating factors (i.e. factors that could explain a possible causal relationship) include: 1) more relaxed pace and personal attention at County Hospital, 2) fewer patients with severe infections so lower probability of infection.
d)Possible approaches:
1)
You would need to find a pool of patients willing to participate in an experiment in which the hospital to which they are sent is selected randomly with no weight given to the patient's preferences.
Obstacle: hard to find willing patients, so few that they might not be typical of population.
2)
Select the hospital randomly for each patient.
Obstacle: Such a procedure would not be acceptable ethically.
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