Which of the following describes a variable?

A variable is fundamentally defined as an attribute that can take on different values or characteristics among subjects in a study. This means that it is not constant; instead, it can change depending on the individuals or observations being examined. For example, height, age, or test scores can vary from one participant to another, making them all variables.

The other answers suggest fixed characteristics or constants, which do not accurately describe a variable. While the correct answer highlights the variability inherent in a variable, the other options imply stability or lack of change, which is contrary to the essence of what a variable represents in research and statistics. Understanding this concept is crucial for data analysis and interpretation, as the ability to measure and assess changes in variables is at the heart of statistical investigation.