Introduction
Definitions

Arithmetic average

Also known as the arithmetic mean. A mathematical representation of the typical value of a series of numbers computed as the sum of all the numbers in the series divided by the count of all numbers in the series.

Suppose we have sample space {x1,.....,xn}. If n numbers are given, each number denoted by xi, where i = 1, ..., n, the arithmetic mean A is the [sum] of the xi's divided by n or defined via the equation:

Harmonic average

Also known as the harmonic mean. The harmonic mean is appropriate for situations when the average of rates is needed. The harmonic mean H of the positive real numbers x1, x2, ..., xn > 0 is defined as follows:

Median

A median is a numeric value separating the higher half of a sample, a population, or a probability distribution, from the lower half. The median of a finite list of numbers can be found by arranging all the observations from lowest value to highest value and picking the middle one. If there is an even number of observations, then there is no single middle value; the median is then usually defined to be the average, or mean, of the two middle values.

Percentile

A percentile, or centile, is the value of a variable above which a certain percentage of observations fall. For example, the 20th percentile travel time is the value above which 20 percent of all the observations may be found. For example, a percentile of 50 is the median travel time for a route and a percentile of 90 means that that particular travel time has been achieved by at least 90% of all the vehicles on the route.

Segment

A segment is a piece of road. It can also be referred to as an edge or a road-element. Segments are of random length and are created internally by TomTom Traffic Stats at every location where a road attribute changes. Examples of road attributes changing are as follows:

  • speed limits changing.
  • street names changing.
  • city borders being crossed.
  • house number format changing.

Hence segments have no fixed length.

Standard deviation

Standard deviation is a widely used measure of the variability or dispersion. It shows how much variation there is from the "average". A low standard deviation indicates that the data points tend to be very close to the average or mean, whereas high standard deviation indicates that the data is spread out over a large range of values.

A slightly different explanation uses a normal distribution or bell-shaped curve. When the data samples are tightly bunched together and the bell-shaped curve is steep, the standard deviation is small. When the samples are spread apart and the bell curve is relatively flat, that tells you that you have a relatively large standard deviation.

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