What term describes a property or characteristic that does not vary across a sample?

The term that describes a property or characteristic that does not vary across a sample is "constant." In research methods, a constant is a value that remains unchanged throughout the study or dataset, providing a stable reference point. Constants are essential in research because they allow researchers to isolate the effects of other variables by holding certain factors steady.

In contrast, a variable represents a property or characteristic that can change or vary among participants or observations. Independent and dependent variables are specific types of variables that relate to the effects being studied; the independent variable is manipulated to observe its impact on the dependent variable, which is measured. The concept of a constant is foundational in research methodology, as it ensures that variations observed in the dependent variable can be attributed to changes in the independent variable rather than extraneous factors.