ISR10 Evaluation of Document Retrieval Systems chapter Joseph John Rocchio Harvard University Gerard Salton Use, reproduction, or publication, in whole or in part, is permitted for any purpose of the United States Government. 5-25 or n +1 recall error = - 0 (5.18) 2 Thus the integral of the difference between the recall function for a perfect retrieval and the recall function of an actual retrieval oper- ation is the difference between the actual average rank ([OCRerr]) of the members of the set of relevant documents and the average rank (n0+1.)/2 which would obtain under perfect retrieval. This parameter may be normalized to the range C - ering the case fQr which the rank of every member of D is greater than every member of D This is clearly the case error; therefore: 1 by consid- numerically of maximum n 0 1 \[OCRerr] - n +1 max recall error =7 ½ N - (ii' 2 i=1 Hence: = n10[OCRerr] no (N + N - n0 + i)$ - n0 +2 1 N-n 0 - n[OCRerr] +2 1 re (5.19) n N-n 0 * is a normalized index of the recall error. As this parameter measures recall error, it' is desirable to reverse it. Therefore: r = 1 h[OCRerr]-_(nO +1 fl) n ½ N-n L `0 *([OCRerr].2o)