statistics review 2 samples and populations统计评估2样品和数量.pdf

Available online /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 popu- Strictly speaking, the theoretical Normal distribution is contin- lation that is ultimately of interest to the investigator (e.g. uous, as shown in Fig. 1. However, data such as those shown intensive care unit [ICU] patients, patients with acute respira- in Fig. 2, which presents admission haemoglobin concentra- tory distress syndrome, or patients who receive renal replace- tions from intensive care patients, often provide an excellent ment therapy). It is seldom possible to obtain information from approximation in practice. every individual in the population, however, and attention is more commonly restricted to a