Why might the results of a controlled experiment differ from the results of a natural experiment when trying to answer a given question?

The control experiments have control variable the natural experiment control by nature lacks this

Explanation:

When a n experiment is set up to answer a particular questions,by subjecting the investigating subjects or individuals to experimental factors beyond the control of the investigator but control by nature,such experiment is said to be Natural.Since the investigator lacks control over the factors determining the experiments.,then natural experiment are observational studies.Therefore they are said to lack controlled variables.

In order to test hypothesis or theories,experiments can be set up by the investigator under certain  regulated factors.Thus the variable to determine the effect on the subjects or individual  of the investigating conditions can be manipulated by the investigator.  Hence it can be said to have a control variable.The experiments is called control experiment.

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i guess you forgot putting it.