IX-43

                          Request improved by     Request not
                         association over null    improved by
                                                  association

 Request improved by              16                    8         24
 indexing over null

 Request not improved                                             18
 by indexing over null             9                    9

                                  25                   17         42


         a)  Improvements of Association Methods over Indexing


                            Request greatly       Request not
                             improved by        greatly improved
                             association         by association

 Request greatly
 (rank recall up .1)               4                    5          9
 improved by indexing

 Request not greatly                                   23         33
 improved by indexing             10

                                  14                   28         42

       b)  Large Improvements of Association Metnods over Indexing


Contingency Tables for Co-Variation of Indexing and Association Methods


                             Table 13