Systematic Errors Systematic errors are harder to find. Your data and results may look consistent and reproducible. Here you may be doing something you are not aware of that is causing all your measurements to be off the same amount. This is a systematic error because all your data is affected the same amount, and in the same direction. 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.