Safety of anesthetics. The death rates of surgical patients differ for operations in which different anesthetics are used. An observational study found these death rates for four anesthetics:

Anesthetic: Halothane Pentothal Cyclopropane Ether Death rate: 1.7% 1.7% 3.4% 1.9%

This is not good evidence that cyclopropane is more dangerous than the other anesthetics. Suggest some lurking variables that may be confounded with the choice of anesthetic in surgery and that could explain the different death rates.

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