In statistics and probability theory, the median is a measure of central tendency that represents the middle value separating the higher half from the lower half of a data sample, a population, or a probability distribution. It is the point above and below which half (50%) of the observed data falls, and so represents the midpoint of the data. To find the median, the data points must first be sorted or arranged in value order from lowest to highest or highest to lowest. If the number of data points is odd, the median is the middle data point in the list. If the number of data points is even, the median is the average of the two middle data points in the list. The median is a special case of other ways of summarizing the typical values associated with a statistical distribution: it is the 2nd quartile, 5th decile, and 50th percentile. The median can be used as a measure of location when one attaches reduced importance to extreme values, typically because a distribution is skewed, extreme values are not known, or outliers are untrustworthy.