Meaning
Statistical functions representing the proportion of observations below a specific value define the observed behavior of a dataset. An empirical cumulative distribution maps every sample point to its percentile rank without requiring a predefined probability model. This method applies only to independent observations and loses its validity when the dataset contains censored or missing entries.
Ranks define probability.
Step Magnitude
Every individual observation in the sample increases the cumulative value by a fixed increment equal to the reciprocal of the total sample size. When the empirical cumulative distribution reaches its final observation, the total value always equals exactly one. This behavior creates a step function where the height of each vertical jump indicates the frequency of a specific value in the set.
Points with identical values produce a single jump with a height proportional to the number of duplicates. Height determines frequency.
Sample Limit
Statistical precision in this representation improves as the number of observations increases. While a small set of data points might produce a jagged approximation, a large empirical cumulative distribution converges toward the true underlying probability curve. Large samples increase accuracy.
Comparison Utility
Analysts use these functions to determine the similarity between two distinct datasets by measuring the maximum distance between their plotted curves. Such a comparison reveals whether a process has drifted away from its historical baseline or if two different populations share the same underlying characteristics. Distance metrics like the Kolmogorov-Smirnov statistic rely on these distributions to quantify the deviation between observed data and expected models.