A constant, as its name suggests, is something that does not vary or change (or that may not be susceptible to variation or change).


  • A constant has only one attribute or value.
  • The search for constants is the ultimate goal in science. A scientific law (eg light in a vacuum travels at 300,000 km/seg) is a constant. As such, it allows us to predict properties based on such law, to use it as a premise in deductive sciences, and to use it as an assumption in inductive sciences.
  • A main task in experimental research, however, is to control the variability of all but the research variables. This control is done by way of keeping all other variables as constants. Once this is achieved, it is possible to ascertain the relationship between the research variables, as these would be the only variables actually varying.
  • Any variable can be made into a constant by reducing its expression to only one of its values.

For example, we could keep the temperature of a room constant at 35o C during an experiment. In this case, temperature stops being a variable.

  • A constant has no use in statistics. That is, anything that is or remains constant cannot be subjected to statistical analysis. Many researches, however, may take this property as meaning that a given constant is not relevant for predicting something, which is not always the case.

For example, if social research finds that children who don't go to school end up as criminals in adult life, while children who go to school do not, then this variable (child scholarization) can "predict" future criminality. If so, there will also be good reasons to make all children attend school, as this should reduce criminality in the future. Yet, once all children go to school, the original variable does not vary anymore, thus becoming a constant. A constant cannot be used for statistical analysis, thus it cannot be used for predicting future criminality, and, thus, it is removed from statistical models. This may be fine so far as scholarization continues. However, the lack of statistical significance may be interpreted as lack of relevance, which may lead to stopping the intervention, and this to an increase in criminality in the future. In this example, child scholarization, although a constant, predicts future criminality, even when it doesn't seem statistically significant.

How to make a constant

  • A variable can be made into a constant by reducing its expression to only one of its values. Eg, gender can be made a constant by only choosing women for a particular research project; or temperature can be made a constant by keeping it at 35o C throughout an experiment.

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