第八章确定样本计划.pptVIP

样本和抽样的基本概念 总体(population) 样本(sample) 样本单位(sample unit) 普查(census) 抽样误差(sampling error) Defining the Population The entire group under study as specified by the research objectives Supermarkets that are part of chains (Safeway, Publix, Woodman’s) located in Wisconsin. Persons in charge of household financial planning located in Pima County, Arizona Sample and Sample Unit A sample is a subset of the population that should represent the entire group. A sample is said to be “representative” if, in fact, it represents the entire population. A sample unit is the basic level of investigation…a college student, a housewife, a purchasing agent, a supermarket, a bank, etc. Census A census is defined as an accounting of the complete population. Census is taken every 10 years It is very difficult to take a census when the population is large and/or not easily accessed. Sampling Error Sampling error is any error that occurs because a sample is used. Sampling error is caused by two factors: 1. Method of sample selection (the PLAN) and 2. The size of the sample. If the average height in this class is really 5’9” and a sample of the people on the first row shows their average height to be 5’6”, we have sampling error of 3”. Sample Frame The sample frame is a master list of all the sample units in the population. If the population were defined as all chain supermarkets in Wisconsin, then a list containing all such stores would be the sample frame. Sometimes a physical list is not possible. The sample frame for a mall intercept survey would be all shoppers who were walking through the mall on the days data were collected. 样本和抽样的基本概念 总体(population)：是指根据调研计划的目的所规定的研究整体。 样本(sample)：是能代表整体的总体的子集。 样本单位(sample unit)：是调研中最基本的被调查对象。 普查(census)：一种完整总体的说明。 抽样误差(sampling error)：因调查中使用样本产生的误差。 12.2 Reasons for Taking a Sample Taking a census can be very costly if the population is large and/or hard to access. Data analysis with hundreds of thousands of observations, even with to