Which of the following best defines a variable in research?

A variable in research is best defined as an element that can be changed or controlled. This is because variables play a crucial role in experiments and studies, serving as factors that can either be altered to observe potential effects or maintained constant to measure other influences.

For instance, in a scientific experiment investigating the effect of sunlight on plant growth, the amount of sunlight received can be manipulated or controlled by the researcher to determine its impact on growth rates. This manipulative capacity is foundational to experimental design, allowing researchers to establish cause-and-effect relationships.

While it's true that elements that can be measured and elements that affect the environment are relevant to the context of research, they do not fully encapsulate the concept of a variable as effectively as the ability to change or control an element. Measurement focuses on quantification but does not imply any capability for manipulation, and environmental factors can be variables but do not encompass the broader definition.