tailieunhanh - Báo cáo y học: "Statistics review 2: Samples and populations"

Tuyển tập các báo cáo nghiên cứu về y học được đăng trên tạp chí y học General Psychiatry cung cấp cho các bạn kiến thức về ngành y đề tài: Statistics review 2: Samples and populations. | Available online http content 6 2 143 Review Statistics review 2 Samples and populations Elise Whitley and Jonathan Ball Lecturer in Medical Statistics University of Bristol UK Lecturer in Intensive Care Medicine St George s Hospital Medical School London UK Correspondence Editorial Office Critical Care editorial@ Published online 7 February 2002 Critical Care 2002 6 143-148 2002 BioMed Central Ltd Print ISSN 1364-8535 Online ISSN 1466-609X Abstract The previous review in this series introduced the notion of data description and outlined some of the more common summary measures used to describe a dataset. However a dataset is typically only of interest for the information it provides regarding the population from which it was drawn. The present review focuses on estimation of population values from a sample. Keywords confidence interval normal distribution reference range standard error In medical and other research there is generally some population that is ultimately of interest to the investigator . intensive care unit ICU patients patients with acute respiratory distress syndrome or patients who receive renal replacement therapy . It is seldom possible to obtain information from every individual in the population however and attention is more commonly restricted to a sample drawn from it. The question of how best to obtain such a sample is a subject worthy of discussion in its own right and is not covered here. Nevertheless it is essential that any sample is as representative as possible of the population from which it is drawn and the best means of obtaining such a sample is generally through random sampling. For more details see Bland 1 . Once a representative sample has been obtained it is important to describe the data using the methods described in Statistics review 1. However interest is rarely focused on the sample itself but more often on the information that the sample can provide regarding the population of interest. The .