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  1. #1
    Moderator
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    Sep 2005
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    272

    The new co-occurence table explorer, info on c-coefficient

    Dear ATLAs.ti users,

    in case you are wondering what is caculated when you click on the option c-coefficient in the new table cooccurence explorer, here is the answer:

    You find a detailed description at:

    http://www.miislita.com/semantics/c-index-1.html

    Here the passage that explains the calcuation behind the coefficient:

    Normalized Co-Occurrence

    The global co-occurrence I have described is an absolute or unnormalized metric. Note that different set of queries (k1, k2, and k12) retrieve different sets of documents (n1, n2, and n12). For the purpose of comparing term co-occurrences between different queries and sets of retrieved documents, one would need to normalize these within a practical scale. Normally one would prefer to compare values running within a practical scale, for instance running from 0 to 1, such that one would be able to compare relative, normalized co-occurrence.

    This normalized co-occurrence is what I define as the "Co-Occurrence Index" or C-index. In the case of pairwise co-occurrence, i.e., co-citation frequency between two and only two terms k1 and k2, the C-index is given by

    Eq 1: C12-index: n12 / (n1 + n2) - n12

    the results are between 0 and 1, where

    * c12 = 0 when n12 = 0; i.e., k1 and k2 do not co-occur (terms are mutually exclusive).

    * c12 > 0 when n12 > 0; i.e., k1 and k2 co-occur (terms are non mutually exclusive).

    * c12 = 1 when n12 = n1 = n2; i.e., k1 and k2 co-occur whenever either term occurs.


    kind regards,

    Susanne
    Dr. Susanne Friese
    Qualitative Research & Consulting
    http://www.quarc.de

  2. #2
    Member
    Join Date
    Sep 2009
    Posts
    2
    Hello

    I have a related question about the new co-occurence table. I understand the index as described as above but what are the small circles in the upper right hand corner supposed to mean? Also - in your example above co-occurence is an index from 0-1. I have values well over 1. What is this telling me?

    Thank you - sorry if any of these have been answered elsewhere but I couldn't find the information in any of the manuals or online discussions.

    Ann

  3. #3
    Member
    Join Date
    Sep 2009
    Posts
    2
    Hi again

    Sorry - I just remembered a related question. In some of the cells a pop-up window appears telling me "Occ-ratio=12 exceeds limit (5)". I have no idea what this means, can anyone help me?

    Thanks again

    Ann

  4. #4
    ATLAS.ti Executive
    Join Date
    Sep 2005
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    297
    Both issues will be explained shortly. Proimised!
    - Thomas

  5. #5
    Member
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    Apr 2009
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    6
    Quote Originally Posted by Thomas Muhr View Post
    Both issues will be explained shortly. Proimised!
    - Thomas
    Thomas,

    Please include an explanation of the "Best Occurrences" feature as well. Having read through sources identified by Suzanne, I think I get it but there's nothing like having the programmer explain how they implemented the algorithm to bring it all together. I think this is particularly important if you the idea is to get wide spread usage of features in question.

  6. #6
    ATLAS.ti Executive
    Join Date
    Sep 2005
    Posts
    297
    Curtis,
    just in case you subscribed to this thread. I published some details on the Cooc Table elsewhere:
    http://forum.atlasti.com/showthread.php?t=4939.
    Regarding the best pairs ranking: it simply sorts all pairs (the cooc table - like any 2-dimensional table - consists only of pairs) by their coefficient and delivers as many pairs (from best to worst) as you indicate when starting this function (currently: CTRL-key + Export to Excel button).
    - Thomas

  7. #7
    Senior Member
    Join Date
    May 2006
    Posts
    90
    Hi does this work when the PDs are video coding?
    Ole

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