Plan for the next few weeks:SamplingCharacteristics of sample statistics (estimators)(Estimators are random variables.)Confidence Interval EstimationHypothesis TestingSamplingTo some extent this is where “statistics” (as a discipline) really starts. The goal is to make meaningful statements about populations. But statisticians, or those using statistical analysis, must use samples to draw inferences about the population, because it usually is impractical (timeconsuming and expensive) to scrutinize the whole population.Drawing a sampleOur goal is a sample that is representative of the population. The surest way to achieve this goal is to draw asimple random sample. In a simple random sample the probability that an element (person, car, whatever) is in the sample is 1/N.1
There are many variations on simple random sampling, but all involve a strong element of randomness. Many polls, for example, rely on a technique known as multistage cluster sampling.