# Floor Effect: Definition

The floor effect is what happens when there is a lower limit below which data levels can’t be measured. Usually, this is because of inherent weaknesses in the measuring devices or the measurement/scoring system. This lower limit, which affects dependent variables, is referred to as the floor, and can badly skew a data distribution if not accounted for.

The floor effect is also sometimes called the basement effect.

## Examples of the Floor Effect

A simple example of a floor effect might be found in scores of a mathematics test given to a set of incoming freshmen at a college. Suppose this test consists of five difficult math problems. If only a small amount of the incoming freshmen are capable of making any attempt at the questions, the test has a very high floor and is not useful in differentiating the majority of the students.

Now suppose all the questions on it were tough, perhaps higher-level statistics. Then it would not be useful in separating those who failed high school math from those who aced Calculus, as all students would probably end up with an extremely low score.

A test which included a few questions in Calculus might be successful in identifying those who took honors math, but the high floor would still make it useless in identifying those students who never went higher than advanced mathematics but were very good in everything they undertook.