What type of variable is manipulated by the researcher to observe its effect on another variable?

The independent variable is the one that is manipulated by the researcher in an experiment. This manipulation is crucial as it allows the researcher to observe how changes in the independent variable affect another variable, known as the dependent variable. For example, if a researcher is studying the effect of different amounts of sunlight on plant growth, the amount of sunlight is the independent variable, and it is altered to see how it influences plant growth, which is the dependent variable.

In contrast, the dependent variable is what the researcher measures in the experiment to see if it is affected by the independent variable. Extraneous variables are outside factors that could potentially influence the outcome of the study but are not the primary focus. Control variables are factors that are kept constant to ensure that the results are due to the manipulation of the independent variable and not other influences. Thus, identifying the independent variable is essential for establishing causation in experimental research.