Question

Emilio's teacher told his class that a controlled experiment's results are valid only if one factor in the experiment is changed and all the other factors remain constant. Why is this statement true?
Changing several different factors in an experiment takes too much time.

Changing several different factors in an experiment takes too many controls.

When only one factor is changed, you don't need to use a control.

When only one factor is changed, you can be more certain that it caused the results.

Answer 1

Actually, two of the statements can be argued to be true:
1)Changing several different factors in an experiment takes too many controls.

This means that for every factor that is changed you need a control which has all the other factors stable - but with many factors, this might be undoable.

2) - and this is the best answer:
When only one factor is changed, you can be more certain that it caused the results.

If this factor is the only thing that changes, you can safely assume that it caused the results!

Answer 2

A.  When only one factor is changed, you can be more certain that it caused the results.

There are several ways to make sure the results of an investigation are valid. First, you and others can try to repeat the experiment. In addition, if it is a controlled experiment, you can make sure you have a control, only one independent variable, at least one dependent variable, and constants.

It is especially important to use only one independent variable because when only one factor is changed, you can be more certain that it caused the results. If you change multiple factors, you won't know which one was responsible for the change.