Generally speaking, there are mainly three kinds of variables involved in scientific experiments: independent variables, dependent variables and control variables  Independent variables are variables that are manipulated by the experimenter in an experiment  A dependent variable is a variable that changes as the independent variable changes
Control variables refer to potential factors or conditions other than independent variables in an experiment that affect experimental changes and results
To study the effect of sugar mill turnover on sugar production, the unit price of sugar is the control variable and sugar production is the independent variable