-Characteristics of Multi-search engines.

I have tried to put together a list of the different elements which one might expect to appear on a multi-search engine page. Unfortunately few, if any of the multi-search engines exhibit all of these elements, and indeed some will have very few of them.
The number of search engines that a Multi-search engine will use
The number of search engines which are used varies dramatically - the smallest in the sample that I looked at only referred to half a dozen, while the largest in the sample gave me access to over one thousand search engines, or database front ends. This is no real indicator of quality however; it depends much more on the search engines which are used (and also the variety) rather than the sheer number. I would much prefer to use a Multi-search engine which referenced a small number of what I would consider to be high quality search engines than a much larger number of engines that I did not really know or trust.
Nonetheless, I think it is an acceptable criteria to use when evaluating the effectiveness of a Multi-search engine; while more is not necessarily better, less could certainly be considered worse. While I would not normally evaluate success in terms of the number of hits this is one of the reasons why one would use a Multi-search engine, so I feel that it is justified.
The elements of the Internet which are searched.
It seems almost automatic these days to regard the phrase 'Search the Web' as a synonym for 'Search the Internet'. Of course, while that is understandable, given the hype and attention surrounding the World Wide Web, it behoves us to remember that there are a number of other aspects of the Internet which deserve consideration as well, such as Usenet newsgroups, or individuals email addresses and so on. Multi-search engines are at the mercy of the search engines they choose to reference, but given that there are a good number of these which concentrate on specific aspects such as those just mentioned there is no reason why they should not be made available for searching as well.
Any words, all words, phrase searching.
Again, there is little that the Multi-search engine can do directly about this since they are unable to affect the internal workings of individual search engines. However, it is an option that should be offered to the end user; if one search engine can search on a phrase out of the list available it seems short sighted not to offer this. Other engines on the list will simply ignore the phrase aspect and search on the words using an implied OR. If this is not given as an option though, it reduces the effectiveness of those search engines which can undertake phrase searching. It seems to be an obvious point, but is one which was overlooked by some of the Multi-search engines which I looked at
Boolean operators, truncation and proximity searching.
The very same comments can be made here as just given above. A Multi-search engine should provide and reflect the variety of approaches made available by the engines it references, but all too often this was not the case.
Focussing a search.
There are of course many occasions when the user will not wish to do a global search, but will want to focus on one aspect specifically, such as searching in a specific domain (such as .com) or a geographical area (such as Europe). Yet again some search engines allow the user to focus the search this way, but this is not always reflected in the interface offered by the Multi-search engine.
Choice of subject area.
This approach is very familiar to anyone who has ever used the Index approach to search engines, by taking a broad subject area and choosing various subheadings until the specific subject is reached. It is well known to all of us in the information profession that much of the time we will not want everything on a subject, but will wish to focus on the medical or legal aspects for example. Some Multi-search engines did offer the ability to choose a specific subject focus or indeed provide a subset of search engines which cover a particular subject area, and the The Big Hub deserves to be singled out here for being quite superb in this approach.
Time taken and hits returned.
Two important elements here which both approach the problem of the amount of time that it takes to run some of these searches. A major disadvantage of using a Multi-search engine is that you are very much left in the hands of the engines referenced. If they decide to take a long time to return a result, or they are particularly comprehensive you may be sat twiddling your thumbs while they work. By limiting the search either by number of hits or by getting the search to end after a particular period of time you are able to exert at least a little control over the whole process. The danger here of course is that you are not going to get the same level of comprehensiveness that you might get otherwise, but at least you are being given the choice
Display
Many search engines will allow you one of three display modes; brief, normal or verbose. Your choice is likely going to depend on what you actually want from the search, and the variety can be quite helpful in some circumstances.
Collate results.
When using a single search engine it is not uncommon to find the same site turning up as a hit several times - de-duping does not seem to be that much of a priority for a lot of developers! This problem is exacerbated when you do a multi-search; it can be annoying to retrieve what appears to be a reasonable number of hits, only to find that there are a great many duplicates in the list. In my opinion, one of the keys strengths of a good Multi-search engine should be that it is able to collate the results, de-dupe and then display. Unfortunately however, it appeared to be very uncommon to find one which did.
Help screens/FAQ's
It is slightly distressing to see so many Internet retrieval engines attempt to give users the impression that searching is a very simple process, when of course we know that its rather more complex than that. All too often I would log onto a Multi-search engine page to find no instructions, no hints on how to create a better or more effective search, and no way of identifying how many search engines were used. Indeed, the lack of such information was quite astonishing. Perhaps its just me, but if I'd taken a lot of time to create a Multi-search interface, I'd want everyone to know who I was, how I had done it and why it was effective. Its possible that the producers of these facilities have rather smaller egos than I, but I tend to think that it is related rather more to laziness than anything else.