What does the term 'manipulation' refer to in experimental research?

In the context of experimental research, the term 'manipulation' specifically refers to the alteration of the independent variable to observe its effects on the dependent variable. This is a fundamental aspect of experimental design because researchers change or manipulate one factor (the independent variable) to determine if it causes any changes in another factor (the dependent variable).

By manipulating the independent variable, researchers create different conditions or groups within an experiment, allowing them to establish cause-and-effect relationships. This manipulation distinguishes experimental research from correlational studies, where researchers merely observe relationships without actively changing any variables.

The other options, while related to the broader concepts of experimental research, do not define 'manipulation.' Control of extraneous variables is essential for maintaining internal validity and ensuring that the results are due to the manipulation itself. Random sampling techniques improve the representativeness of a sample but are not directly related to the manipulation of variables within an experiment. Measuring dependent variables is crucial for assessing the effects of the independent variable, but this measuring action does not pertain to the concept of manipulation itself.