Simple Random Sampling

829 Words4 Pages
INTRODUCTION 1. Objective: Take a sample from the population, measure some characteristic on each of the sampled units, and use this information to estimate (infer) the characteristic in the entire population. 2. Simple random sampling is the most basic sampling procedure to draw the sample. 3. Simple random sampling forms the basis for many of the more complicated sampling procedures. 4. Simple random sampling is easy to describe but is often very difficult to carry out in the field where there is not a complete list of all the members of the population. DEFINITION: A simple random sample is a sample of size n drawn from a population of size N in such a way that every possible sample of size n has the same chance of being selected. 5. Note that this definition requires that we know the population size N. ASSUMPTIONS FOR SIMPLE RANDOM SAMPLING Simple random sampling is one form of the general set of sampling procedures referred to as probability sampling. Probability sampling procedures must meet 4 criteria (Cochran, 1977:9): 1. We can define the set of distinct samples which the procedure is capable of selecting. 2. Each possible sample has assigned to it a known probability of selection. 3. We select one of the samples by a random process in which each sample receives its appropriate probability of being selected. 4. The method for computing the estimate must lead to a unique estimate for any specific sample. For any sampling procedure of this type we can calculate the frequency distribution of the estimates that it generates if repeatedly applied to the same population and therefore determine bias and variance of the estimator. In general we do not assume that the underlying population follows a normal distribution, but in order to calculate bounds and confidence intervals from single samples it may be useful to assume that the estimates follow a

More about Simple Random Sampling

Open Document