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通常,大样本标准差的计算多采用简捷的分组计算法。笔者拟采用实例,就标准差的另一种简捷方法——频数累计法作如下介绍。今抽取100株树木,实测树高,经分组如表的前三列。经分组计算得平均树高×=7.28,标准差S=0.39。试用频数累计法计算平均树高和标准差。解:计算格式如表。这里需稍加说明的是,频数累计第Ⅰ列中令频数最多的25所在行为0;频数累计第Ⅱ列中令频数25及上下各一行为0。h为组距。Ⅹ_0为频数最多的树高值。另外,令A=48,B=47,C=27,D=27。(分别为频数累计而来)计算结果表明,频数累计法与分组计算法
In general, the calculation of standard deviation of large samples using more simple group calculation method. I intend to use examples to standard deviation of another simple method - Frequency Cumulative Method for the following description. Today extracted 100 trees, the measured tree height, grouped as the first three columns of the table. The average tree height calculated by grouping × = 7.28, standard deviation S = 0.39. Trial frequency cumulative method to calculate the average tree height and standard deviation. Solution: Calculate the format as table. It should be noted here that the cumulative number of columns in the first column of the total frequency of 25 is 0; the cumulative number of columns in the second column of the frequency 25 and the upper and lower rows of 0. h is the group distance. Ⅹ_0 is the most frequent tree height value. In addition, let A = 48, B = 47, C = 27, D = 27. (Respectively for the cumulative frequency) calculated results show that the frequency of the cumulative method and group calculation method