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1、电大电大试验设计与生物统计试验设计与生物统计作业二（第三到四章）作业二（第三到四章）1 1、什么是变数？变数有哪几种？、什么是变数？变数有哪几种？变数是表示其变异的观察值的总称为变数。变数分为数量变数和质量变数两大类。数量变数又分为连续性变数和间断性变数（又称离散性变数）两类。数量变数是指以数量大小表示的变数，来自对数量性状的测量和计数。连续性变数指通过量长度、测体积或称重量等量测方法所得的数据。其观测值并不限于整数，在两个相邻的数值间可以有微量差异的其它数值存在。常见的连续性变数有作物的株高、穗长、叶面积、穗粒重、产量等。间断性变数（或离散型变数）是以计数的方式获得的数据。其观察值只能以整数
2、表示，如水稻基本苗数、单株分蘖数、每亩成穗数、每穗小穗数、单株粒数、花瓣数、单株分枝数、主茎叶片数等都只能是整数。 。质量变数又称属性变数，质量变数来自对属性性状的观测记载，这类性状只能观察而不能测量。如花的颜色、芒的有无、果实形状的圆扁等。要从这类性状获得数量资料，可采用下列两种方式：计数，即在一定范围内计数具有该种性状和不具有该种性状的个体数，这种通过计数的方法获得的资料又称次数资料。质量性状数量化。如小麦芒性可分为无芒、短芒与长芒三类，若用 0 表示无芒，用 1 表示短芒，用 2 表示长芒，则从质量性状上获得了数量化的记载，就可得到和数量性状相似的资料。2 2、什么是总体、样本、参数、统
3、计量？、什么是总体、样本、参数、统计量？总体是指一个统计问题研究对象的全体，它是具有某种（或某些）共同特征的元素的集合。参数是描述总体特征的数，如反映数据的集中趋势的总体平均数、反映数据的变异程度的总体方差、反映不同总体的相关关系的相关系数等。样本是从总体中抽取的部分个体组成的集团，是总体的代表。由样本所有个体计算出来的特征数称为统计数。统计数是随样本个体组成不同而变化的，是一个变量。3 3、什么是算术平均数？有何特征和优缺点？、什么是算术平均数？有何特征和优缺点？算术平均数：是指资料中各观测值的总和除以观测值个数所得的商，简称平均数或均数，记为。算术平均数的特征：算术平均数大小受每个值的影响
4、。如果是 n1个数的平均数，是1x1x2xn2个数的平均数，那么全部 n1+n2个数的算术平均数是加权平均数：。各观察值与x212211 nnxnxn 平均数之差（离均差）的总和等于 0。离均差平方和最小。若 A 为任意常数：当=XA,则 x； 当=X.A 时，,则；当=X/A,则。平均数是有单位的数值，其单位的Axxm xAxx/ xAxx数值，其单位与原资料相同。算术平均数优点是计算简单，而缺点是计算平均数时没有考虑到近期的变动趋势，因而预测值与实际值往往会发生较大的误差。 4 4、如何编制次数分布表？、如何编制次数分布表？编制次数分布表的步骤：求全距：全距是指一批数据中最大值与最小值之间
5、的差距，又称极差。定组数：就是要确定把整批数据划分为多少个等距的区组。定组距:以全距和组数来确定分组的组距。一般原则是取奇数或 5 的倍数，如1，3，5，7，9，10 等。写出组限：为了确定各个观察值的归属，每组必须设有界限。组限是每个组的起止点界限，最小值称为下限，最大值称为上限。求组中值：组中值是各组的组中点在量尺上的数值，其计算公式为：组中值=（组实上限+组实下限）2。不同的组距以及不同的组限，必然会产生不同的组中值。如果希望每组的组中值恰好为整数便于后续运算，那么，组距选择为奇数是最好的。编制次数分布表：参照如下次数分布表组别组限组中值次数16.9,7.57.215 5、正态总体的抽样
6、分布的特征？、正态总体的抽样分布的特征？（1） 从一个正态总体抽取的样本，无论样本容量大或小，其样本平均数 的抽x样分布必为正态分布，具有平均数和方差，记为 N(, )。xnx22n2（2）从一个非正态总体抽取的样本，不一定服从正态分布，但当样本容量 n 增大时，从该总体抽出的样本其平均数 的抽样分布趋近于正态分布，具平均数 和方x差，这就是统计学的中心极限定理。 n26 6、如何运用标准正态分布计算概率？、如何运用标准正态分布计算概率？根据中心极限定理，无论原总体分布是否为正态分布，只要样本容量足够大，其的分布都可看作正态分布。在实际应用上，只要 n30 就可以应用这一定理。知道x了 抽样分
7、布的规律及其参数，任何样本 值的对应的概率就可很容易地计算出来了。平均数 的标准化离差分布将 转换为 u，再查表求概率。xxnxxux )()(27.5,8.17.848.1,8.78.45Visa-free policy brings Chengdu biz, tourism boost. Making national headlines several times, Chengdus 72-hour visa-free policy has attracted wide attention from both Chinese and foreign experts and busines
8、smen since it took effect on Sept 1 last year. The program permits citizens from 51 countries and regions including the United States, Australia, Canada and Japan who have valid visas and flight tickets to a third country to spend three days in the city. The capital of Sichuan province is the first
9、city in the western region of China to offer foreign tourists a three-day visa and the fourth nationwide to adopt the policy following Shanghai, Beijing and Guangzhou. Li Zhiyong, deputy dean of the tourism institute at Sichuan University, said the move “contributes to a large increase in the number
10、 of overseas tourists and raises the citys level of internationalization“. “The policy will also bring direct economic revenue,“ Li said. “Chengdu has many cultural legacies and is also a paradise for panda lovers with the worlds largest breeding and research center. Three days are long enough for f
11、oreign visitors to visit those iconic tourist spots,“ he noted. The city is home to the remains of the Jin sha civilization that dates back more than 3,000 years as well as the Qing cheng Mountains and the Du jiang yan irrigation system. Qing cheng has long been recognized as the birthplace of Taois
12、m, Chinas ancient indigenous religion, while Du jiang yan is considered to be the oldest functioning water-control project in the world. Chengdu ranked third in tourist facilities, management and services among 60 Chinese cities in a customer satisfaction survey released last year. But, Li added tha
13、t efforts are still needed to develop more tourism products, improve English services and provide accurate translation of traffic signs and scenic billboards. Zhao Yun, chairwoman of British Chamber of Commerce Southwest China, told China Daily that his colleagues found the policy very convenient. “
14、A British client once flew here and stayed for just one day to check her ordered goods,“ she said. Zhao was born in Shanxi province, but she has lived in Chengdu for more than 10 years. “My life was like a running race moving from place to place. I also lived in Beijing and Shanghai before,“ she sai
15、d. “But Chengdu is a place that you never want to leave once settling down. It is now my second hometown,“ she said. If the environment is further improved, the city will attract more people to visit and live, with the 72-hour visa-free policy and compelling conditions in transportation, culture, cl
16、imate and cuisine, he said. Foreigners also gave positive feedback on the policy. A spokesman from Dell Inc said the company has a global hub of operation in Chengdu, so the three-day visa “has an immediate and positive influence on the companys business development“. Rudy Buttignol, president of the public broadcasting company in British Columbia, Canada, said his work requires frequent travel to Chengdu a
