[MUSIC] A population refers to the complete set of all items which are of interest of the investigator. The population size, which is indicated by the symbol N, capital letter, can be very large, up to infinite. A sample is a subset or portion of the population with the sample size given by the symbol n. Examples of populations include the following, all potential customers of a new service, all the banks in a given economic system, all the students within a school. The aim we have in mind while applying the statistical process is to make a statement based on the sample data that can be generalized to the population. This means that our analysis on the sample data should have some validity about the population at large. In other words, we need a sample that is representative of all the population. This is why the type of data used and the choice of the sample are of crucial importance. How can we reach that goal? We first must follow in the sample selection process, the principle of randomness. Let us see the random sampling first. Simple random sampling which is more common as random sample is a procedure used to select a sample of an object from a population in such a way that the choice of each member of the population is strictly by chance. The selection of each member is not influenced by the selection of any other member. Each member of the population is equally likely to be chosen. And finally, there is the same chance of selection for every possible sample of a given size n. Systematic sample, suppose that the population list is arranged in some fashion and connected with the subject of interest. Systemic sampling involves the selection of everyday item in the population. We have that j is the ratio of the population size, N, to the sample size, n, that is j=N/n. Randomly selecting number from 1 ot j in order to obtain the first item to be included in your systematic sample. Suppose that a sample size of 100 is the size and the population consist of 5000 names in alphabetical order. This means j = 50. Randomly select a number from 1 to 50. If your number is 20, select it and every 50th number, giving the systematic sample of element numbered 20, 70, 120, 170, and so forth, until all 100 items are selected. A systematic sample is analyzed in the same fashion as the simple random sample, on the basis that relative to the subject of interest. The population listing is already in random order, however, a bias may arise if there is a hidden link between the ordering of the population and the subject under study. If this is the case, then the systematic sampling employed can be distorted. Systematic samples provide a good representation of the population if there is not cyclical variation in the population. [MUSIC]