All search engines are not the same and all search engines do not return the same results. Ask each of the big four search engines the same ques­tion and you’ll get four very dif­fer­ent sets of answers. Well duh… 

But just how dif­fer­ent are the results? Dif­fer­ent Engines, Dif­fer­ent Results, pub­lished in April by the good folks at Dog­pile gives some hard numbers.

Over the set of all returned first page results 88.3% of first page results are unique to the search engine that returned them and only 1.1% of the first page results turn up in all four engines.

This is a great study for fer­ret­ing out lit­tle nuggets that will astound and amaze the naive searchers. Even the DH who has to lis­ten to me bab­ble on about this stuff and who, being an ubergeek him­self, ought to know bet­ter thought that there was­n’t much dif­fer­ence in the results of one SE vers­es another.

Anoth­er favorite num­ber is from Fig­ure 2.

Google’s index­ing cov­er­age of the “Total Web”(1) is giv­en as 69.6%.

Do the math. Google does­n’t cov­er 30.1% of the Web.

That said the study is prone to a bit of an apples and oranges con­fu­sion. Some­times they sep­a­rate out spon­sored and non-sponsored results and oth­er times they don’t.(2)

Cum gra­no salis. Though they cred­it researchers at Queens­land U. and Penn State this research is in aid of a par­tic­u­lar com­mer­cial ven­ture — Dog­pile. (One of my fav agre­ga­tors, though.)

(1) Actu­al­ly the term used in the fig­ure “Total Web” is mis­lead­ing. It should be “Total Vis­i­ble (to Search Engines) Web” There’s a whole ‘nother web out there that the search engines can’t see. The authors get it right in the text.

(2) For exam­ple in Fig­ure 5 they list the per­cent­ages of first page results (of those returned by all four SEs) that you would miss if you had only used one SE. (All around 70%.) But they don’t call out spon­sored vs. non spon­sored results. So what? So… spon­sored results can only appear in results pool of the SEs that the spon­sors have cho­sen to pay for. By def­i­n­i­tion, there are cer­tain results that can not appear in mul­ti­ple search engines.

(Why is all the good stuff in the footnotes?)