Copyright © Allyn & Bacon (2007) Using a Random Number Table Graziano and Raulin Research Methods: Appendix D This multimedia product and its contents are protected under copyright law. The following are prohibited by law: (1) Any public performance or display, including transmission of any image over a network; (2) Preparation of any derivative work, including the extraction, in whole or in part, of any images; (3) Any rental, lease, or lending of the program.
Copyright © Allyn & Bacon (2007) Random Number Table The random number table in Appendix D contains 10,000 random digits The random number table in Appendix D contains 10,000 random digits In a random number table, In a random number table, –all digits are equally probably, and –the probability of any given digit is unaffected by the digits that precede or follow it
Copyright © Allyn & Bacon (2007) Using the Table Select a starting point Select a starting point –by closing your eyes and pointing randomly on a page –selecting randomly a starting line (0-199) Then move forward or backwards to obtain the random digits desired Then move forward or backwards to obtain the random digits desired Different approaches depending on the randomization task desired Different approaches depending on the randomization task desired
Copyright © Allyn & Bacon (2007) Example: Sampling Participants Number each participant from 1 to N Number each participant from 1 to N If N is a 3-digit number, move forward in the table 3 digits at a time; if N is a 4-digit number, move 4 digits, etc. If N is a 3-digit number, move forward in the table 3 digits at a time; if N is a 4-digit number, move 4 digits, etc. Record each non-repeated number, which will correspond to one of the participants Record each non-repeated number, which will correspond to one of the participants That list of numbers describes your sample That list of numbers describes your sample
Copyright © Allyn & Bacon (2007) Practical Steps Random Numbers (from text) Random Numbers (from text) To sample from 300 participants, move in blocks of 3-digits, selecting each non- repeated number between 1 and 300 (underlined) To sample from 300 participants, move in blocks of 3-digits, selecting each non- repeated number between 1 and 300 (underlined) 219, 224, 088, 256, 186, 191, 192
Copyright © Allyn & Bacon (2007) Example: Assigning Participants Task: Randomly Assign participants to 4 groups Task: Randomly Assign participants to 4 groups Steps: Steps: –Find a starting point and decide whether you will move forward or backward –Write down every digit between 1 and 4 in the order they appear as you move –Assign participants to groups in the order in which the digits (1-4) appear in your list
Copyright © Allyn & Bacon (2007) Practical Steps Random Numbers (from text) Random Numbers (from text) To randomly assign participants to one of four groups, select the underlined digits To randomly assign participants to one of four groups, select the underlined digits
Copyright © Allyn & Bacon (2007) Example: Assigning Participants Task: Randomly assign participants to four groups in blocks of four Task: Randomly assign participants to four groups in blocks of four Steps: Steps: –Same procedure as in previous slide EXCEPT that your digits are recorded in blocks of 4 (1, 2, 3, & 4) –Ignore digits that already appear in the block until the block is complete, then repeat the process for the next block
Copyright © Allyn & Bacon (2007) Practical Steps Random Numbers (from text) Random Numbers (from text) To randomly assign 20 participants in blocks of 4, select the underlined digits To randomly assign 20 participants in blocks of 4, select the underlined digits 1324; 4231; 4321; 1342; 4123
Copyright © Allyn & Bacon (2007) Random Number Generator Random number generator program is available on the textbook website Random number generator program is available on the textbook website It will produce any custom sequence you need and write it to a file, which you can print out to guide your participant selection or assignment It will produce any custom sequence you need and write it to a file, which you can print out to guide your participant selection or assignment
Copyright © Allyn & Bacon (2007) Using the Random Number Generator Program Download the program from the website Download the program from the website Double-click the filename (randnum.exe) to run the program Double-click the filename (randnum.exe) to run the program Follow the directions Follow the directions Output is written to a text file that can be printed Output is written to a text file that can be printed
Copyright © Allyn & Bacon (2007) Opening Screen
Copyright © Allyn & Bacon (2007) List of Random Numbers
Copyright © Allyn & Bacon (2007) How Many Random Numbers Do You Want?
Copyright © Allyn & Bacon (2007) Give It Your Request
Copyright © Allyn & Bacon (2007) And Get the List
Copyright © Allyn & Bacon (2007) Assign Participants to Conditions
Copyright © Allyn & Bacon (2007) Assigning Participants Tell the program how many conditions Tell the program how many conditions Tell the program how many participants Tell the program how many participants Hit return to get your assignments Hit return to get your assignments
Copyright © Allyn & Bacon (2007) Random Assignment List
Copyright © Allyn & Bacon (2007) Summary Random selection or assignment of participants will increase the external and internal validity of your study, respectively Random selection or assignment of participants will increase the external and internal validity of your study, respectively Random number table provides the random digits necessary to do any randomization task Random number table provides the random digits necessary to do any randomization task Your text provides a random number generator program on the textbook website Your text provides a random number generator program on the textbook website