一、总体的分布密度函数上一讲中我们以油松苗木的样本资料说明了随机性、随机变量和频率曲线的概念。通过“样本数据落入某固定区间的频率当样本容量增大时趋于稳定”这一现象,引进了概率的概念。概率是随机试验的结果——“事件”发生可能性大小的一个数量指标。随机变量根据取值情况可主要分为两大类。取值为有限个或可数个孤立数值,如病腐木株数、发芽种子的粒数等称为离散型随机变 First, the overall distribution of density function In the previous lecture, we illustrate the concept of randomness, random variables and frequency curve with sample data of Pinus tabulaeformis seedlings. The concept of probability is introduced by the phenomenon “the frequency at which sample data falls into a fixed interval tends to be stable when the sample size increases.” Probability is the result of a randomized trial - a quantitative measure of the probability of occurrence of an “event.” Random variables according to the value of the situation can be divided into two categories. The value is a finite number or a few isolated values, such as the number of diseased rotten trees, the number of seeds germinated and so called discrete random variable