Which type of variable remains unchanged and consistent across different observations?

The correct choice is a constant because it refers to a variable that does not change in value throughout the course of an experiment or research study. In research, a constant is something that researchers aim to control and keep the same in order to ensure that any changes in the dependent variable can be attributed solely to manipulations of the independent variable. For example, if a study examines the effect of a new therapy on anxiety levels, a constant might be the age range of participants to ensure that this factor does not influence the results.

In contrast, the dependent variable is what researchers measure in the experiment, and its value can change based on the manipulations of the independent variable. The independent variable is what researchers manipulate to observe its effect on the dependent variable, and it can vary across different conditions or observations. Value or value labels refer to the specific numerical or categorical representations assigned to variables, rather than being a variable that remains consistent throughout the observations. Therefore, a constant is the only option that embodies the concept of being unchanged and consistent across different observations.