第四章抽样与估计.ppt

4-1 Chapter 4: Sampling and Estimation 4-2 Need for Sampling ? Very large populations ? Destructive testing ? Continuous production process The objective of sampling is to draw a valid inference about a population. 4-3 Sample Design ? Sampling Plan – a description of the approach that will be used to obtain samples from a population ? Objectives (总体中重要的参数估计、或总体之间是否存在显著差异) ? Target population ? Population frame (目标总体完整的名单) ? Method of sampling ? Operational procedures for data collection ? Statistical tools for analysis 4-4 Sampling Methods ? Subjective ? Judgment sampling ? Convenience sampling (易获得性) ? Probabilistic ? Simple random sampling – every subset of a given size has an equal chance of being selected 4-5 PHStat Tool Random Sample Generator ? PHStat menu > Sampling > Random Sample Generator Enter sample size Select sampling method 4-6 Excel Data Analysis Tool Sampling ? Excel menu > Tools > Data Analysis > Sampling Specify input range of data Choose sampling method Select output option 4-7 Other Sampling Methods ? Systematic sampling ? Stratified sampling ? Cluster sampling ? Sampling from a continuous process 4-8 Errors in Sampling ? Nonsampling error ? Poor sample design ? Sampling (statistical) error ? Depends on sample size ? Tradeoff between cost of sampling and accuracy of estimates obtained by sampling 4-9 Estimation ? Estimation – assessing the value of a population parameter using sample data. ? Point estimate – a single number used to estimate a population parameter ? Confidence intervals – a range of values between which a population parameter is believed to be along with the probability that the interval correctly estimates the true population parameter 4- mon Point Estimates ?