In a research experiment, which variable is manipulated by the experimenter?

The independent variable is the one that is manipulated by the experimenter in a research experiment. This is the variable that the researcher deliberately changes to observe its effect on another variable, which is typically the dependent variable. By controlling and varying the independent variable, researchers can test hypotheses about causal relationships.

In an experiment, the independent variable is crucial because it allows for the establishment of cause-and-effect relationships. For instance, if a researcher is studying the impact of different amounts of study time on test scores, the amount of study time would be the independent variable, as it is what the researcher alters to observe variations in test scores, the dependent variable.

The dependent variable is observed and measured for changes in response to the manipulation of the independent variable. Control variables, which need to be kept constant, are not manipulated but are essential for ensuring that any changes in the dependent variable are due solely to the manipulation of the independent variable. Extraneous variables are those that may interfere with the results but are not the focus of the experiment; these need to be controlled to avoid confounding the results.