# Tag Info

Two devices are in common use to present univariate distributions. The cumulative form, or "cumulative distribution function" (CDF), gives--for every real number $x$--the chance (or frequency) of a value less than or equal to $x$. The "density" form, or "probability density function" (PDF), is the derivative (rate of change) of the CDF. The PDF might not exist (in this restricted sense), but a CDF always will exist. The CDF for a set of observations is called the "empirical density function" (EDF). Thus, its value at any number $x$ is the proportion of observations in the dataset less than or equal to $x$.