2.2: 什么是频率分布

A frequency is the number of times a value of the data occurs. The sum of all the frequency values represents the total number of students included in the sample. It is commonly used to group data of quantitative types. Frequency distributions can be displayed in a table, histogram, line graph, dot plot, or pie chart, just to name a few. A histogram is a graphical representation of tabulated frequencies, shown as adjacent rectangles, erected over discrete intervals (bins), with an area equal to the frequency of the observations in the interval.

In a frequency distribution table, the data values are grouped into classes of equal widths. The class boundaries are individual values chosen to separate classes (often being the midpoints between upper and lower class limits of adjacent classes), while the smallest and largest observations in each class are called class limits. Frequency distributions can typically have between 5 and 20 classes, all with equal widths, mutually exclusive, continuous, and exhaustive.