The main purpose of an experiment is to test a specific hypothesis, usually by only testing one factor or vari. This implies that for an experiment to be successful, the researcher or scientist needs to make most of the variables constant. Besides this, it is common one variable or factor is manipulated (independent variable), and this is used to determine how the main factor studied (dependent variable) is affected.
The previous ideas imply the factors involved in an experiment need to be carefully monitored or controlled to guarantee only the main factor that interests the researcher is studied. This is highly complex and one of the most challenging factors because it is difficult to notice and control all factors in an experiment. According to this, it is true the most difficult part of an experiment is to design an experiment that tests only one factor.
