医学统计学英文课件-SamplingErrorandConf.pptVIP

* Sampling Error and CI * There are two random samples drawn from the two populations respectively, of which the sample sizes, sample means and sample standard deviations are ; ; . It is expected to estimate the 95% confidence interval for the difference of average red cell counts between healthy male and female residents. * Sampling Error and CI * Example 3.3(Cont. of Example 3.2) Assume there are two big samples randomly drawn from the two populations respectively, of which the sample sizes, sample means and sample standard deviations are Please estimate the 95% confidence interval for the difference of average red cell counts between healthy male and female residents again. (0.29, 0.67) (1012/L). (0.16, 0.80) (1012/L). Comparing with the last estimate based on small samples the precision is improved. * Sampling Error and CI * 3.5 Confidence Intervals for Probability and the Difference between Two Probabilities * Sampling Error and CI * When sample size is small, the 95% and 99% confidence interval of ? can be obtained from special statistical table; when sample size is big enough, ? can be estimated by normal approximation for the distribution of P. * Sampling Error and CI * The confidence interval of the population probability: , * Sampling Error and CI * Confidence intervals for two population probabilities * Sampling Error and CI * Vocabulary t distribution standard normal deviation standard t deviation degrees of freedom probability density critical values two-side inequality t 分布 标准正态偏差 标准 t 偏差 自由度 概率密度 临界值 双侧 不等式 * Sampling Error and CI * Vocabulary confidence interval confidence level pooled estimation small sample large sample normal approximation population probability width precision 置信区间 置信水平 合并估计 小样本 大样本 正态近似 总体概率 宽度 精度 * Sampling Error and CI * Sampling Error : For several samples