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Simple Random Sample

  1. Mar 31, 2012 #1
    David C. White owns a small advertising business. He has twelve employees. The names
    of the employees are given below.

    1. Becker
    2. Brown
    3. Chasten
    4. Ito
    5. Kim
    6. Spitzer
    7. Taylor
    8. Walt
    9. Wang
    10. Zhang
    11. Zhao
    12. Zhu

    Use the list of random digits below to select a simple random sample of three names from
    the list of employees. Start at the beginning of the list and use the numerical labels
    attached to the names.

    11920 14931 20051 27498 12009 45287 71753 31137 20495 05907

    the answer is Zhao, Becker, Kim

    I don't know where to start, I do not understand what the list of numbers represent? Anyone mind guiding me through this problem?

  2. jcsd
  3. Mar 31, 2012 #2


    User Avatar
    Science Advisor

    Hey Larrytsai.

    If your table values are between 00000 and 99999 then each value represents a random number between those values. In terms of a uniform distribution your first number would correspond to 11920/10000 = 0.1192.

    Now if you want to choose a data entry you have multiply this normalized number by the number of entries you can select from. Then you floor the answer and add one to get the index of the entry. For this example 0.1192 x 12 = 1.4304 so our index is Floor(1.4304) + 1 = 2 which corresponds to the 2nd name.

    All this is doing is you get a distribution that approximates a uniform distribution and then you have to make sure your random number is between 0 and 1 and then you basically allocate each block of your distribution to an index. For example for 10 data items (0-0.999999 etc) is allocated to data 1, (0.1,0.1999999etc) allocated to data 2 and so on. and this is why we use the floor function.
  4. Apr 1, 2012 #3
    thank you so much!
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