Identify the independent variable : The amount of pollution produced by cars was measured for cars using gasoline containing different amounts of lead.
An independent variable is the potential stimulus or cause, usually directly manipulated by the experimenter, so it could also be called a manipulative variable.
A dependent variable is the response or measure of results.
Which is the potential cause, and which measures the results?
the independent variable is the amount of pollution produced
and the dependent variable was gasoline containing different lead
The independent variable in this scenario is the amount of lead in the gasoline used in cars.
The independent variable in this scenario is the amount of lead in the gasoline used by the cars.
To identify the independent variable, you need to ask yourself: what is being manipulated or controlled in the experiment? In this case, the researchers are controlling the amount of lead in the gasoline, and they are interested in observing how this manipulation affects the amount of pollution produced by cars. Therefore, the independent variable is the amount of lead in the gasoline.