集中趋势
众数
内涵：出现频次最多的变量取值
众数组的组中值：<span class="equation-text" contenteditable="false" data-index="0" data-equation="{{组上限+组下限} \over 2}"><span></span><span></span></span><br>
中位数
偶数中位数：<span class="equation-text" data-index="0" data-equation="M_e=\cfrac{x_{n \over2} +x_{n+1 \over2}}n " contenteditable="false"><span></span><span></span></span><br>
分组中位数：<span class="equation-text" data-index="0" data-equation="M_e=L+\cfrac{{N \over2} -Cf\uparrow}n h" contenteditable="false"><span></span><span></span></span>
算数平均值
<span class="equation-text" data-index="0" data-equation="\bar{x}={\sum_{i=1}^n x_i \over n}" contenteditable="false"><span></span><span></span></span>
<span class="equation-text" data-index="0" data-equation="\bar{x}={\sum_{i=1}^k n_ix_i \over \sum_{i=1}^k n_i}" contenteditable="false"><span></span><span></span></span>
分组算数平均值：<span class="equation-text" data-index="0" data-equation="\bar{x}={\sum_{i=1}^k n_ib_i \over \sum_{i=1}^k n_i}" contenteditable="false"><span></span><span></span></span>（<span class="equation-text" contenteditable="false" data-index="1" data-equation="b_i"><span></span><span></span></span>为组中值）<br>
离散趋势
异众比率
<span class="equation-text" data-index="0" data-equation="\gamma={{N-f_m} \over N}" contenteditable="false"><span></span><span></span></span>
内涵：表明众数代表性，异众比率越小，众数代表性越高<br>
极差
内涵：变量的取值范围
R=最大值-最小值<br>
四分位差
<span class="equation-text" contenteditable="false" data-index="0" data-equation="未分组：Q=Q_75-Q_25"><span></span><span></span></span>
分组：<br>
下四分位数：<span class="equation-text" contenteditable="false" data-index="0" data-equation="L+\cfrac{{N \over4} -Cf\uparrow}n h"><span></span><span></span></span>
上四分位数：<span class="equation-text" contenteditable="false" data-index="0" data-equation="L+\cfrac{{3N \over4} -Cf\uparrow}n h"><span></span><span></span></span><br>
平均差
内涵:离差绝对值的平均值
<span class="equation-text" data-index="0" data-equation="D={ \sum_{i=1}^n |x_i-\bar{x}|\over n}" contenteditable="false"><span></span><span></span></span>
方差
<span class="equation-text" data-index="0" data-equation="原始数据计算：\sigma^2={ \sum_{i=1}^n {(x_i-\bar{x})}^2\over n}" contenteditable="false"><span></span><span></span></span><br>
<span class="equation-text" data-index="0" data-equation="频次数据计算：\sigma^2={ \sum_{i=1}^k {(x_i-\bar{x})}^2n_i\over \sum_{i=1}^k n_i}" contenteditable="false"><span></span><span></span></span>
标准差
<span class="equation-text" data-index="0" data-equation="原始数据计算：\sigma=\sqrt{{ \sum_{i=1}^n {(x_i-\bar{x})}^2\over n}}" contenteditable="false"><span></span><span></span></span>
<span class="equation-text" data-index="0" data-equation="频次数据计算：\sigma=\sqrt{{ \sum_{i=1}^k {(x_i-\bar{x})}^2n_i\over \sum_{i=1}^k n_i}}" contenteditable="false"><span></span><span></span></span>
