London School of Hygiene & Tropical Medicine, University of London

MSc Clinical Trials by Distance Learning

CT102 Basic Statistics for Clinical Trials

BS06 Principles of Statistical Inference. Point and Interval Estimation

Sample Estimates and Sample Distributions

We select a sample because we want information on a particular feature of the target population; for example, the average walking distance of people with peripheral vascular disease or the effect of screening for abdominal aortic aneurysm in men aged 65-74.

Since we have no means of finding this feature directly, we collect information on a random sample, taken from the target population, and use it as our best estimate of the population value.

To clarify the distinction between the population and the sample values we generally use Greek letters like mu (mu) or pi (pi) for the population value, and Roman letters like x or p for the sample value. Remember from BS02 that the sample mean of a variable x is denoted x bar.

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