QQ圖幾年前就聽過，但不知道代表什麼，也沒有動力去弄明白，現在明白了；Q代表quantile，圖上的每一個點有個內在屬性，就是兩組資料的分位點是相同的；比如說某個點是資料集1的上四分位點，那麼也一定是資料集2的上四分位點； The quantile-quantile (q-q) plot is a graphical technique for determining if two data sets come from populations with a common distribution; 

由此可以推斷：兩個資料集的資料一定是排好序的；

QQ圖還會有一個直線進行對比； A 45-degree reference line is also plotted. If the two sets come from a population with the same distribution, the points should fall approximately along this reference line. The greater the departure from this reference line, the greater the evidence for the conclusion that the two data sets have come from populations with different distributions.