|< Day Day Up >|
Some website search facilities exhibit seemingly nonsensical , "crazy" relationships between the search criteria you give them and the results they return. For example, suppose you searched at an online pet store for " siamese cats" and got 42 hits, then searched for "cats" and got no hits. You'd probably say "Huh?," not believe the results of the second search, and try it again. Unfortunately, this sort of "crazy" behavior is common enough that I consider it a blooper.
"Crazy" search behavior was also found at Erlbaum.com, the website of Lawrence Erlbaum Associates (Figure 5.37). Its Search page provides text fields for Title, Author, and ISBN, and menus for Subject. Suppose you want to check whether developmental psychologist Dan Osherson has published any books with Erlbaum. If you search for Author = "osherson," you get nothing. If you try again, adding a criterion, such as Primary Subject = Developmental/ Lifespan Psychology, you get a long list of books, but none by Osherson. With more criteria, you get more hits, which are not books by the specified author. Huh?
There are two possible explanations for Erlbaum.com's odd behavior. The most plausible explanation is that when site users specify more than one search criterion, Erlbaum's search facility looks for books matching any of the criteria. In contrast, most people would expect it to look for books matching all of the criteria at once. Another possible explanation is that normally it would look for books satisfying all the criteria, but when there are no books matching one of the criteria, it (erroneously) ignores that criterion and just uses the others, in this case, Primary Subject. Whatever the cause, the behavior of this search facility does not match what most people would expect.
At RadioShack.com, when you search for "videotape," you find no videotape, just three products that are related , more or less, to videotape (Figure 5.38[A]). But if you search for "video tape" (two words), you find several categories of products, including videotape. Huh? "Videotape" is at least as common a spelling as "video tape," if not more so (See also Blooper 35: Search Myopia: Missing Relevant Items, in this chapter).
As the two examples of this blooper suggest, "crazy" search behavior has diverse causes, and therefore diverse solutions.
Erlbaum.com's odd behavior is probably caused by combining search criteria nonintuitively: returning items matching any of the criteria, even if they match only the optional criteria and not the "main" one. When people add optional criteria to a search specification, it is more reasonable to assume that they want to find items matching all of the criteria. The sidebar (Tech Talk: Combining Search Criteria) discusses this in more technical terms.
When specifying criteria for a computer search, people often specify more than one criterion. Sometimes they want the search to find items matching any of the criteria, and sometimes they want it to find only items that match all of the criteria.
Computer scientists have technical terms for these two ways of combining search criteria: OR and AND .
OR: Find items that match any of the criteria. For example, search for books authored by Osherson OR books about developmental psychology.
AND: Find items that match all of the criteria. For example, search for books that are authored by Osherson AND are about developmental psychology.
Using this terminology, we can say that when people give multiple search criteria, they normally expect them to be ANDed unless they say otherwise . Any search function that ORs multiple search criteria without providing a strong indicator that it is doing so will seem odd to users.
The implication for design: Search functions should AND criteria together, at least by default and perhaps with no option to do otherwise. If it is necessary to let users specify ORed searches, provide it as an option.
At RadioShack.com, a difference in results between searching for "videotape" versus "video tape" is most likely due to inadequate indexing of the data. The solution: adding all plausible spellings as keywords.
The unifying principle for avoiding "crazy" search behavior is to design search facilities to behave according to user expectations. That means finding out what users expect or at least testing the facility to see if it often makes users say "Huh?"
|< Day Day Up >|