Statistics 312 3 Sampling 1 Sampling A non probability sample is one in which the judgment of the experimenter the method in which the data is collected or other factors could affect the results of the sample Judgment Samples Any sample based on someone s expertise about the population is known as a judgment sample Voluntary Samples Voluntary samples involve open solicitation of input and attract only those who are interested in the subject matter Convenience Samples Surveys where the concern is primarily on the ease with which the sample is taken is called a convenience sample A probability sample is one in which the chance of selection of each item in the population is known before the sample is picked Simple Random Samples If a probability sample is chosen in such a way that all possible groupings of a given size have an equal chance of being picked and if each item in the population has an equal chance of being selected then the sample is called a simple random sample Systematic Samples Suppose we want to pick a probability sample of 50 people from a list of 1 000 registered voters in a community This means that we plan to sample 50 1000 or 1 20th of the population One way of doing that is by using a random number table to pick one of the first 20 voters on our list If the table gave us the number 16 then the 16th voter on the list would be the first to be selected We would then pick every 20th name after this random start the 36th voter the 56th voter to produce a systematic sample Statistics 312 3 Sampling Read pp 10 15 Problems 1 8 1 9a 1 10a on last two use MINITAB Read pp 15 26 Optional 2
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