Dear Ovid Customer:

OvidSP’s Basic Search continues to generate a lot of buzz in the librarian community. One specific feature that is causing a lot of interest is the new Include Related Terms option. Some customers have asked: Why do I sometimes get fewer search results when I include related terms? The following explanation should shed some light on this.

The NLP-based Basic Search was designed to find the most relevant results, not all results. Since some searches could return an almost infinite set of results, the system has a manageable cut-off point of 500 results ranked by relevancy.

Each search result is assigned a score based on its relevancy to the search query and all results with the same score are grouped together. The number of groups (let’s call them “Scoring Groups”) varies depending on the number of results that are assigned the same score. We stop after the first group that brings the total result count past 500. If that group is large, the ending count may be a lot higher than 500.

Example:
The query "computed tomography {No Related Terms}" returns 900 equally relevant results in MEDLINE. The query doesn't provide much information, so the system can't whittle the result down to the 500 or so that it prefers to return; all 900 results are equally relevant, so they're all returned.

Here is another hypothetical example. Suppose that for a particular search, the scoring of the results returns the following:

Five of the results for this query were assigned a score of “1”; 14 a score of “2”; 37 a score of “3”; and so forth. We can see that the “Scoring Group” that brings the total over 500, Scoring Group “7”, contains 367 results, bringing the total number of results OvidSP shows to 805. If the last group, the one with a score of “7” had returned only 200 results, the total number of results shown would have been 638 (438 + 200). If Scoring Group “6” had included enough results to bring the total to over 500, say 359 for example, the total would have been 508 (149 + 359). No results from Scoring Group “7” would have been included.

Please note: the Scoring Groups are a “behind-the-scenes” tool and do not represent the number of stars assigned to a particular result in the result set and which range from 5 to 1 for each result from a Basic Search.

Why was 500 chosen as the cutoff point for Basic Search results?
Based on our extensive end-user research, we found that users who are looking for the most relevant articles to their query− rather than doing an exhaustive literature search− rarely look at more than 100 results before accepting what they have, refining their search, or trying a new search. On the other hand, we want to have a sufficient amount of results. Based on this research, it was determined that five hundred is an appropriate set of results for Basic Search.

If you have any questions about Basic Search or any other aspect of OvidSP, please contact your Ovid Account Representative or support@ovid.com. If you haven’t already done so, contact support@ovid.com for access to OvidSP. Please be sure to visit the OvidSP Resource Center (you now have open access to the OvidSP Resource Center—username and password are no longer required!) to sign up for a live training session, request a customer launch kit, and download informational materials. Plus, view the new online demo!

Regards,

Wolters Kluwer Health - Ovid