Slide 1-2 Chapter 1 The Nature of Statistics Section 1.2 Simple Random Sampling
Slide 1-3 Three Methods for Obtaining Information Census – obtaining information for the entire population of interest This method can be time consuming, costly, impractical, or even impossible.
Slide 1-4 Three Methods for Obtaining Information Sampling – obtaining a sample from the population to draw conclusion about the entire population. Two sampling procedures: Representative sample – should reflect as closely as possible the relevant characteristics of the population under consideration. Examples of samples that would not be representative of the population. Surveying people regarding political candidates as they enter or leave an upscale business location Surveying the readers of a particular publication to get information about the population in general Polling college students who live in dormitories to obtain information of interest to all students
Slide 1-5 Three Methods for Obtaining Information Probability sampling – a random device (tossing a coin, table of random numbers, number generator) is used to decide which members of the population will constitute the sample.
Slide 1-6 Three Methods for Obtaining Information Experimentation – there are three basic principles of experimental design. Control Randomization Replication This method will be introduced throughout the book.
Slide 1-7 Simple Random Sampling Simple Random Sample There are two types of simple random sampling. One is simple random sampling with replacement, whereby a member of the population can be selected more than once; the other is simple random sampling without replacement, whereby a member of the population can be selected at most once. The Inferential techniques considered in this book are intended for use with Simple Random Sampling. Simple random sampling: A sampling procedure for which each possible sample of a given size is equally likely to be the one obtained. Simple random sample: A sample obtained by simple random sampling.
Slide 1-8 Simple Random Sampling (without replacement) Oklahoma State Officials: The top five Oklahoma state officials are: Governor (G), Lieutenant Governor (L), Secretary of State (S), Attorney General (A), and Treasurer (T) List 10 possible samples (without replacement) of size three that can be obtained from the population of five officials. GLS, GLA, GLT, GSA, GST, GAT, LSA, LST, LAT, SAT What are the chances of GLS procedure being used? 1/10 What are the chances of GLA procedure being used? 1/10 … This would be true for all the options on the list.
Slide 1-9 Sampling Methods Random samples – is a sample selected in such a way that every member of the population has an equal chance of being selected. i.e., the process of selecting the sample does not favor any member of the population, either intentionally or inadvertently. If a sample is not random, then it is said to be biased. Random Samples are selected using chance methods or random methods. Obtaining a simple random sample by picking slips of paper out of a box is usually impractical, especially when the population is large, and could be a bias sample.
Slide 1-10 Random-Number Tables Fortunately, we can use several practical procedures to get simple random samples. We can now use computers or calculators to generate random samples. One common method involves a table of random numbers – a table of randomly chosen digits, as illustrated in Table 1.5.
Slide 1-11 Table 1.5 Random numbers
Slide 1-12 Random-Number Generators Nowadays, statisticians prefer statistical software packages or graphing calculators, rather than random-number tables, to obtain simple random samples. The built-in programs for doing so are called random-number generators. When using random-number generators, be aware of whether they provide samples with replacement or samples without replacement.