If a variable cannot be removed during an experiment (such as rainfall variations on crop growth), how can researchers know if that variable is causing the observed effect or if the thing they are studying (such as fertilizer) is causing the effect?

Use of a control group

Step-by-step explanation:

A common use of a control group is an experiment in which the effect of a treatment is uncertain and correlations are used to measure the impact of the treatment between the control group and the experimental group.

For example, in a pharmaceutical study to decide the efficacy of a new medicine on migraine treatment, the new drug will be administered to the experimental group and a placebo (a drug that is inert or assumed to have no effect) will be administered to the control group.

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