What serves as a standard of comparison to evaluate the effect of the independent variable on the dependent variable?

There exists the controlled group of the experiment, where this group receives the placebo, known as the placebo effect or the substance that has actually no effects.

The independent group is the manipulated group which receives the experiment.

Variables are observable and measurable objects used in a study.
Independent variables are those variables manipulated to produce a desired or predicted outcome whereas the dependent variable is the variable that receives the treatment and produces the product.