For example, Age and Gender might be used as independent variables to predict the age of death or life expectancy (dependent variables).
In experimental designs, the independent variables are manipulated by the researcher (e.g., different dosages of a drug). In quasi-experimental and non-experimental designs, the independent variables may be naturally-occurring, non-manipulated variables which are measured and used to predict variations in the dependent variables.
--Example--: Question: Does soda erode rocks just as it does to teeth? Answer: Independent Variable- Whether or not rocks erode in soda. (What are you testing?)
Dependent Variable- The rate of erosion. (What are you measuring?)