SIMPLE RANDOM SAMPLING_stud

SIMPLE RANDOM SAMPLING_stud - SIMPLE RANDOM...

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SIMPLE RANDOM SAMPL ING_stud .doc Jan 25’10 THE SIMPLE RANDOM SAMPLE DEFINITION. Statistical inference is a procedure by which we reach a conclusion about a population on the basis of the information contained in a sample that has been drawn from that population . (RECALL: sample is a subset , or part of a population.) There are many kinds of samples that may be drawn from a population, but only scientific samples can be used for making valid inferences about a population. The simplest of them is the simple random sample . DEFINITION. If a sample of size n is drawn from a population of size N (N > n) in such a way that every element in the population has an equal chance of being chosen as a part of the sample, then such a sample is called a simple random sample . Correspondingly, every possible sample of size n has the same chance of being selected. (A size of the population (or a sample) is the number of entities in it). {In general, a procedure used to collect the sample data is called sampling plan or sample design [2].} The mechanics of drawing a sample in accordance with the above definition is called simple random sampling . The sampling may be performed with replacement , or without replacement . The sampling WITH replacement assumes that every member of a population is available at each draw. For example, let us consider the sampling which involves selecting (from the shelves in a hospital’s medical records department) a sample of [enumerated – M.V.] charts for collecting information of some kind about patients. The sampling with replacement assumes that we select a chart to be in the sample, record the data of interest, and return the chart to the shelf . In such a case, the “population” of charts remains the same, and every chart may be drawn again on some subsequent draw, and the same data about the same patient will again be recorded. In
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This note was uploaded on 11/24/2011 for the course MATH 3000 taught by Professor Kzaer during the Spring '05 term at St. Johns College MD.

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SIMPLE RANDOM SAMPLING_stud - SIMPLE RANDOM...

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