Are anesthetics safe? The National Halothane Study was a major investigation of the safety of anesthetics used in surgery. Records of over $850,000$ operations performed in $34$ major hospitals showed the following death rates for four common anesthetics:

There seems to be a clear association between the anesthetic used and the death rate of patients. Anesthetic C appears to be dangerous.

(a) Explain why we call the National Halothane Study an observational study rather than an experiment, even though it compared the results of using different anesthetics in actual surgery.

(b) When the study looked at lurking variables that are related to a doctor’s choice of anesthetic, it

found that Anesthetic C was not causing extra deaths. Describe how a lurking variable could lead to confounding in this setting.

There is a link between the anesthetic used and the death rate of patients in the death rates report of the four common anesthetics from over $850,000$ surgeries conducted in $34$ large hospitals. Anesthetic C, on the other hand, looks to be more harmful.

Observational research looks at people and assesses factors of interest without trying to affect their responses.

The researchers are not attempting to influence the outcome by allocating participants to treatment or control groups at random, but rather by observing death rates. As a result, the research is observational.

The study is described as an observational study in the preceding section. There are a lot of potential confounders here. Surgery is one of the possible confounders. The death rate could be high due to the usage of certain medications, and it's impossible to say whether the data rate is high due to surgery or pharmaceutical use.