Question

Why do all of the parameters, except the independent variable, have to be controlled?

Answer 1

The independent variable is changed by the experimentor, so it does not have to be changed.

Answer 2

To match the cause to its effect

Step-by-step explanation:

The experimenter alters the independent variable with the hopes of collecting data about how the dependent variable changes in response.Other variables have to be controlled so that any changes of the dependent variable are attributed to the known independent variable. If they are not controlled the experimenter has no way of knowing which variable caused the change. The scientific method would be crippled by that.