Someone recently asked me if I thought it was OK to do more than one literature search for her dissertation. Searching is not a science so much as an art. It's a puzzle, a challenge - something to come at from first one angle then another. It's a treasure hunt. It should make your brain ache, and give you a thrill when you finally find what you are looking for.
So how do you search? I like to use a shopping analogy. Going to Google and asking it tell you something about diabetes is information suicide. You'll die under the avalanche of hits, relevant and irrelevant, that it throws at you. It's the equivalent of wandering into Bluewater on a Saturday afternoon thinking that you want to buy a present for your mother. There are just too many things to buy. You can't possibly look at everything so you have to narrow your search.
Do you want to buy your mother jewellery, books, CDs, DVDs, perfume....? How about something nice to wear? Now the first question is where do you look? You can't buy clothes in Boots, Halfords, Waterstones, HMV or Jessops. On the other hand some shops sell just clothes and others while other sell clothes in among other things (Sainsbury's , Tesco, M&S).
As with shopping, so with searching. For evidence you use Cochrane, for policy you choose HMIC, for nursing issues you try Cinahl, for mental health it's Psychinfo. The Sainsbury's option (for some of everything) is Medline - it's a big database and covers most things, although perhaps not in as much depth as specialist databases.
We're going to go into the first ladies' dress shop in the mall. Now a search engine is something like a rather unhelpful shop assistant. If you are vague and say you want something for your mother to wear she will toss back her hair, examine her nails and inform you that there are five floors of ladies' fashion in the store. Too much information.
On the other hand, if you ask if she has any blouses in a size 14, cotton, with three quarter length sleeves, plain, in a dark rose, she'll just say no. She wont tell you that they have the very thing you want in red, or something similar with full length sleeves. So you need to ask a question at a time until you find what she does and doesn't have. Blouses? Yes. In a size 14? yes. Any size 14 blouses in cotton? Yes. And so on.
The same with searching. Type in "diabetes" and you'll get the look of scorn and far too many hits. Race in to Medline requesting a paper published in the UK in the last 6 months on inhaled insulin for women under 25 with children who are failing to keep their diabetes under control and you get a straight "no". You need to build up your search piece by piece.
Perhaps your mother isn't quite so fussy about her sleeves. Rather than asking for blouse, 14, cotton with 3/4 sleeves (the equivalent of using AND in a search) you could try using OR. So - I want a blouse AND it has to be size 14 AND it has to be cotton. The sleeves can be 3/4 length OR full length. The colour could be dark rose OR red. You're expanding your options with OR, your limiting your options with AND.
So, shop number one has a size 14 cotton blouse in dark red with 3/4 sleeves, or one with long sleeves in dark rose. Neither are quite what you are looking for. Do you go home? Certainly not. You treat yourself to a coffee, and maybe a pastry, and plunge into the next shop and start asking the same questions.
If Cinahl doesn't deliver the goods then try Medline. If HMIC is hopeless then try searching the Department of Health website direct.
You may need to think laterally, too. If there is nothing in cotton then do they have other natural fibres? If they say they don't stock blouses, what about women's shirts? Maybe you'd be better off asking for dark pink or crushed raspberry colour instead of dark rose.
Sometimes after a few shops you find you're going round in circles. You keep finding cotton blouses in size 14, but nothing in dark rose or nothing with 3/4 length sleeves. Finally, after visiting several shops, and asking the questions in slightly different ways you realise that 2/4 sleeves just aren't available this year, or that nowhere stocks dark rose blouses.
At this point you probably can stop. It doesn't mean that nowhere has what you are looking for, but you can feel confident that you've looked as much as possible for now, you've done your best. Sometimes we just have to accept that the particular item we had in mind doesn't exist.
Sometimes the papers you do find wont have the answer you want, but will have extra clues. It's like coming home from Bluewater and finding the Boden catalogue on your doormat. In it there is a shirt. It's blue and it's silk - but look at this. Those are 3/4 length sleeves, but what does the description say? It says those are "bracelet length sleeves". Now why didn't you think of that? Looks like you'll be going back to Bluewater tomorrow.