In statistics, the term floor effect refers to when data cannot take on a value lower than some particular number, called the floor.
An example of this is when an IQ test is given to young children who have either (a) been given training or (b) have been given no training. If the test is too difficult (so difficult that no amount of training will affect the ability to carry out the test), both group (a) and group (b) will perform particularly badly. This does not necessarily lead to the conclusion that the training has no effect on the ability to complete the IQ test. In fact, this may lead to a Type II error. The IQ test is too difficult, and by making the questions less difficult, training may have an effect on the ability to complete the IQ score.
Here, the floor effect is the data all hitting the bottom end of the distribution due to the extreme difficulty of the task. A ceiling effect is precisely the opposite - all participants reaching the high end of the distribution (e.g. the test was too easy).
Famous quotes containing the words floor and/or effect:
“The distant box is open. A sound of grain
Poured over the floor in some eagerness we
Rise with the night let out of the box of wind.”
—John Ashbery (b. 1927)
“I care not by what measure you end the war. If you allow one single germ, one single seed of slavery to remain in the soil of America, whatever may be your object, depend upon it, as true as effect follows cause, that germ will spring up, that noxious weed will thrive, and again stifle the growth, wither the leaves, blast the flowers, and poison the fair fruits of freedom. Slavery and freedom cannot exist together.”
—Ernestine L. Rose (1810–1892)