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From |
khigbee@stata.com |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: re: ANOVA model (my mistake) |

Date |
Mon, 30 Sep 2002 15:44:14 -0500 |

In relation to the discussion started by David Airey <david.airey@vanderbilt.edu> I had pointed out that it did not matter if you used a numbering scheme such as A 1 1 1 2 2 2 B 1 2 3 1 2 3 or A 1 1 1 2 2 2 B 1 2 3 4 5 6 when dealing with B nested in A (written B|A in -anova- syntax). I pointed to the discussion of this on page 64 of "[R] anova". David Airey <david.airey@vanderbilt.edu> then presents two data sets with different labeling for the nested term and shows that they produce different results. Let me point out the misunderstanding between what I was saying and the two datasets presented by David. David's first dataset looks like: neuron subject treatm~t measure 1. 1 1 1 1.232982 2. 2 1 1 1.166421 3. 3 1 1 1.674022 4. 1 1 2 1.690412 5. 2 1 2 1.079583 6. 3 1 2 1.983932 7. 1 1 3 -1.573235 8. 2 1 3 2.714028 9. 3 1 3 3.24 10. 1 1 4 1.470877 11. 2 1 4 4.342456 12. 3 1 4 .1263056 13. 1 1 5 3.049922 14. 2 1 5 2.537046 15. 3 1 5 -.7629604 16. 1 2 1 -1.013575 17. 2 2 1 .6785818 18. 3 2 1 -1.619054 19. 1 2 2 1.396539 20. 2 2 2 .9016123 21. 3 2 2 -2.113595 ... and his second looks like: neuron subject treatm~t measure 1. 1 1 1 3.588527 2. 2 1 1 2.431523 3. 3 1 1 1.267083 4. 4 1 2 2.137298 5. 5 1 2 1.644081 6. 6 1 2 4.000641 7. 7 1 3 2.452223 8. 8 1 3 2.811015 9. 9 1 3 2.97793 10. 10 1 4 1.751251 11. 11 1 4 3.431399 12. 12 1 4 .4201414 13. 13 1 5 1.742686 14. 14 1 5 .4739965 15. 15 1 5 1.596641 16. 16 2 1 -.9146303 17. 17 2 1 -.5972514 18. 18 2 1 -1.519495 19. 19 2 2 -.6959237 20. 20 2 2 -.3078359 21. 21 2 2 -.5360426 ... His anova model is: anova measure subject / neuron|subject ... where I put ... so that we can focus on the first part of the syntax that is the important part for this discussion. It is not surprising that the 2 numbering schemes shown by David are not producing the same results. If you look at my little numbering scheme example A 1 1 1 2 2 2 B 1 2 3 1 2 3 versus A 1 1 1 2 2 2 B 1 2 3 4 5 6 which I claim will produce the same results for B|A, you will notice that in the first case the numbering for B is 1 to n within each level of A. The first dataset that David presents has neuron with 1 to 3 repeated many times for the SAME subject. If his numbering scheme for neuron went from 1 to 15 within each subject, then it would produce the same results as his second data set. I hope this clarifies the point I was trying to make about numbering schemes for nested ANOVA models. If not, please email me and I will gladly discuss it with you. Ken Higbee khigbee@stata.com StataCorp 1-800-STATAPC * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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