Simple Random Sampling

When a census of the entire population of interest is difficult to obtain, a sample is often used. There are many sampling designs that can be used to obtain a sample that would hopefully be representative of the population, and among these sampling designs, several allocate the same inclusion probability to each unit in the population. If each unit in the population has the same inclusion probability and all the units are independent, then we have a simple random sample. Another way to formulate this is to state that each sample consisting of a given number of units has the same probability of becoming the selected sample. Keywords: population; sampling design; sampling frame; sampling with replacement; sampling without replacement