lecture12_2slides

lecture12_2slides - Statistics 528 - Lecture 12...

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Statistics 528 - Lecture 12 1 Statistics 528 - Lecture 12 Prof. Kate Calder 1 Randomization How do we randomly assign the experimental units or subjects to the different treatment groups. Idea: “draw names out of a hat” In practice, 1. Use a random number tables. 2. Use statistical software. Statistics 528 - Lecture 12 Prof. Kate Calder 2 A table of random digits is a list of the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, that has the following properties: 1. The digit in any position in the list has the same chance of being any one of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. 2. The digits in different positions are independent in the sense that the value of one has no influence on the value of the other. As a result, Any pair of random digits has the same chance of being any of the 100 pairs: 00, 01, 02, …, 98, 99. Any triple of random digits has the same chance of being any of the 1000 triples: 000, 001, 002, …, 998, 999. Any so on…
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Statistics 528 - Lecture 12 2 Statistics 528 - Lecture 12 Prof. Kate Calder 3 Using a table of random digit (Table B): 1) Assign every experimental unit a numerical label starting with 1 (or 01 or 001, etc. ..). Use shortest possible labels. All the labels should have the same number of digits. 2) Let k be the number of digits in a label and N the number of experimental units available. 3) Suppose we want to assign m experimental units to one group. Start at any row in the table and read across k digits at a time. Record the first m unique values between 1 and N that appear. - Skip any values not in the range 1 to N . - Skip any value that has already been chosen.
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lecture12_2slides - Statistics 528 - Lecture 12...

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