median = 1, 2, 3, 4, 5, => pick the middle one = 3
in our case, "依據主計處的調查,北市的個人月收入部分,依據收入的高低排序,中間值 的金額,大致落在49,532元,這個金額也形成一個收入高低的分野,可區分成前50%、後50%。"
中間值 = median
mean - The sum of a list of numbers, divided by the total number of numbers in the list. Also called arithmetic mean
median - "Middle value" of a list. The smallest number such that at least half the numbers in the list are no greater than it. If the list has an odd number of entries, the median is the middle entry in the list after sorting the list into increasing order. If the list has an even number of entries, the median is equal to the sum of the two middle (after sorting) numbers divided by two. The median can be estimated from a histogram by finding the smallest number such that the area under the histogram to the left of that number is 50%
mode - For lists, the mode is the most common (frequent) value. A list can have more than one mode. For histograms, a mode is a relative maximum ("bump"). A data set has no mode when all the numbers appear in the data with the same frequency. A data set has multiple modes when two or more values appear with the same frequency.
refer to: http://www.shodor.org/interactivate/lessons/introstatistics/