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In descriptive statistics, the quartiles of a ranked set of data values are the three points that divide the data set into four equal groups, each group comprising a quarter of the data. A quartile is a type of quantile. The first quartile (Q1) is defined as the middle number between the smallest number and the median of the data set. The second quartile (Q2) is the median of the data. The third quartile (Q3) is the middle value between the median and the highest value of the data set. In applications of statistics such as epidemiology, sociology and finance, the quartiles of a ranked set of data values are the four subsets whose boundaries are the three quartile points. Thus an individual item might be described as being "in the upper quartile". == Definitions == * first quartile (designated Q1) also called the lower quartile or the 25th percentile (splits off the lowest 25% of data from the highest 75%) * second quartile (designated Q2) also called the median or the 50th percentile (cuts data set in half) * third quartile (designated Q3) also called the upper quartile or the 75th percentile (splits off the highest 25% of data from the lowest 75%) * interquartile range (designated IQR) is the difference between the upper and lower quartiles. (IQR = Q3 - Q1) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「quartile」の詳細全文を読む スポンサード リンク
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