Simple Random Sampling Lecture 7 Section 2 5 Mon Jan 28 2008 Simple Random Sample Simple Random Sample of size n Simple Random Sample A consequence of this is that all individuals in the population have the same chance of being selected for the sample Simple Random Sample However just because a sampling method guarantees that all individuals in the population have the same chance of being in the sample it does not mean that the sample is a simple random sample Selecting a Simple Random Sample Given a population of size N Number the members from 1 to N Use a random number generator such as on a calculator to generate n random integers from 1 to N Selecting a Simple Random Sample The sampling may be done with or without replacement If the sampling is done without replacement then repetitions should be discarded TI 83 Selecting a Sample Suppose that the population size is N 100 Press MATH Use arrow keys to highlight PRB menu Press 5 to select randInt item 5 Enter randInt 1 100 and press ENTER A random number appears Press ENTER repeatedly for more random numbers Example Let the population be the students in this class numbered 1 7 in alphabetical order So N 7 Choose a random sample of size n 3 What is each person s chance of being selected for the sample Getting a Set of Random Numbers To get several random integers at once possibly with repetitions use randInt with a third parameter For example to get 3 random integers from 1 to 7 enter randInt 1 7 3 TI 83 Setting the Seed Enter the desired seed say 48 Press STO Press MATH highlight PRB select rand item 1 Press ENTER The seed is set to 48 Example Set the seed to 48 Then select a random sample of size 3 from the population of the previous example www random org The web site www random org will provide truly random numbers The numbers are integers ranging over any specified interval They can be generated with repetitions or without repetitions You can also do random coin flips
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