We're using swish-e to search a collection of books and I've discovered  
an odd thing with relevance that I'm trying to puzzle out. The  
following search on "freud":

http://texts.cdlib.org/cgi/searchallbooks.pl? 
search=freud&mode=book+text&sort=relevance

returns a list of books, with the 439th result being the book "Freud  
and His Critics". That book is rife with the word, and yet it is ranked  
very low. I have verified that it is not my CGI that is doing anything  
funny, as a command line search provides the same results. Why is that  
particular book ranked so low, when it has something on the order of  
almost twice as many occurrences of the word "freud" in it as the  
top-ranked book?

Thanks in advance for any ideas.
Roy Tennant