One way to check for systematic errors is to run experiments of a different design that should give the same answers. Scientists often do different kinds of experiments to cross check their results. Another way to locate errors is to have an independent investigator repeat your experiments. Others should get the same results you did. Your results can be invalid if your variables are not independent of one another, and you have not noticed this.
Variables are independent if they produce their effects separately from each other.
In other words, changing one variable does not affect changes produced by another variable. The information contained on this page was written by David Morano, Assoc. Professor, Mankato State University, Minnesotta and was included with his permission.