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Sta220 - Statistics Mr. Smith Room 310 Class #10 Section 3.7 3.7 Random Sampling If n elements are selected from a population in such a way that every set of n elements in the population has an equal probability of being selected, then the n elements said to be a random sample. A random sample is likely to be the representative of the population that it is selected from. Most researchers rely on random-number generators to automatically generate a random sample. Random samples are a sampling procedure that will likely lead to the creation of a representative sample. Generation Random Numbers www.random.org TI-84 Go to Math-> PRB-> randInt( Problem Suppose you wish to randomly sample five households from a population of 100,000 households. a) How many different samples can be selected? b) Use a random-number generator to select a random sample. (Table 3.7) a) How many different samples can be selected? Since we want to select 5 households from 100,000, we apply the combinations rule. n=5 N = 100,000 = 100,000 5 = 100000! 5!99,995! = 8.33 x 1022 Calculator: To use the combination rule: 1) Punch in the top number 2) Go to Math->PRB->nCr(#3)->enter 3) Punch in the bottom number Ex.) 100000 nCr 5 = 8.332500029e22 b) Use a random-number generator to select a random sample. (Table 3.7) Once all the number had been generated on paper would arbitrarily select a starting number, say, the random number appearing in the third row, second column. This number should be 48,360. Then we proceed down the second column to obtain the remaining four random numbers. 48,360 93,093 39,975 6,907 72,905 A blind study is a study where the subjects on which the experiment is being conducted do not know into which experimental group they have been placed. Important Dates 1) Assignment 3.6 due 03/17/14 (11:00 p.m.) 2) Assignment 3.7 (Notes Thursday) due by 3/17/14 (11:00 p.m.) 3) Ch. 3 Review Quiz and Ch. 3 Homework Review Due by 3/19/14 (11:00 p.m.) *ACT Tuesday 4) Unit 2 Test 3/21/14