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We need to explain whether 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.

Here,

The experiment deliberately imposes some treatment on individuals in order to observe the responses.

An observational study tries to gather information without disturbing the scene they are observing.

So records are used, no treatment was deliberately imposed on individuals and thus the study is an observational study.

We need to identify the explanatory and response variables in this study.

A response variable is a variable that measures an outcome or result of a study, while an explanatory variable is a variable that we think explains or causes changes in the response variables.

We expect a different anesthetic to affect the death rate, which implies that the explanatory variable is a type of anesthetic and the response variable is the death rate.

We need to explain the concept of confounding in this context and identify a variable that might be confounded with the doctor鈥檚 choice of anesthetic.

Variables are confounded when the effects on a response variable can't be distinguished.

One possible confounding variable is the type of surgery. If one anesthesia is used often with a type of surgery that has a higher death rate anyway, we wouldn't know if the death rate was higher because of the anesthesia type or the surgery type.