It is a parameter of reality and/or can be changed in an experimental study.

They are characterized as independent variables – changed by the examiner; dependent variables – change under the influence of changes in the independent variable; extraneous (side) variables – cannot be controlled, but affect the source of the dependent error; and latent variables – inaccessible to direct measurement. but affect the source of the dependent error; and latent variables – inaccessible to direct measurement. are fixed by the analysis of covariance of the dependent variables; additional variables – external variables that are taken into account in the experiment, etc. etc.