It can have as many as it needs. You can even change different variables at the same time and study their individual influence with proper statistical tools in many type of experiments.
There are three types of variables tested: manipulated variables, controlled variables, and experimental variables.
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In a properly designed experiment, it is important to have at least 2 controlled variables. With two variables you are able to remove one at a time and see the effect in your setup.
An experiment of any kind can have infinitely many variables. A controlled experiment can have just as many, provided that all but one are kept exactly the same.
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There are three types of variables tested: manipulated variables, controlled variables, and experimental variables.
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In a properly designed experiment, it is important to have at least 2 controlled variables. With two variables you are able to remove one at a time and see the effect in your setup.
An experiment of any kind can have infinitely many variables. A controlled experiment can have just as many, provided that all but one are kept exactly the same.
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It depends on the experiment. Normally only one is tested at a time because they can affect the experiment. Variables are tested in a controlled experiment to see whether they affect the outcome and also how.
In a controlled experiment only 1 variable is being tested.
to gather data from data to create an controlled experiment
to gather data from data to create an controlled experiment
to gather data from data to create an controlled experiment
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A controlled experiment might be impossible if there are too many variables that cannot be controlled or if it is unethical or impractical to manipulate certain variables. Additionally, external factors outside of the researchers' control can also make it difficult to ensure a controlled environment for the experiment.