The development over time of such outcome variables are analyzed as if they were normally distributed over the whole period of time.
Cieling flooring effects epidemiology.
A floor effect is when most of your subjects score near the bottom.
Limited variability in the data gathered on one variable may reduce the power of statistics on correlations between that variable and another variable.
However correcting its score for education may create ceiling effects when used for poorly educated people and floor effects for those with higher education.
There is very little variance because the floor of your test is too high.
Sometimes floor and ceiling effects are referred to as lower and upper censoring.
In some fields biology physiology etc the ceiling effect refers to the point at which an independent variable no longer has an effect on a dependent variable when a kind of saturation has been reached e g the phenomenon in which a drug reaches its maximum effect so that increasing the drug dosage does not increase its effectiveness baker 2004.
The mini mental state examination mmse is the most widely used cognitive test both in clinical settings and in epidemiological studies.
The term ceiling effect is a measurement limitation that occurs when the highest possible score or close to the highest score on a test or measurement instrument is reached thereby decreasing the likelihood that the testing instrument has accurately measured the intended domain.
Psychology definition of floor effect.
In most longitudinal epidemiological studies these floor and ceiling effects are ignored.
Ceiling effects and floor effects both limit the range of data reported by the instrument reducing variability in the gathered data.
In layperson terms your questions are too hard for the group you are testing.
This is even more of a problem with multiple choice tests.