  This paper investigates the composition of search engine results pages. We
define what elements the most popular web search engines use on their results
pages (e.g., organic results, advertisements, shortcuts) and to which degree
they are used for popular vs. rare queries. Therefore, we send 500 queries of
both types to the major search engines Google, Yahoo, Live.com and Ask. We
count how often the different elements are used by the individual engines. In
total, our study is based on 42,758 elements. Findings include that search
engines use quite different approaches to results pages composition and
therefore, the user gets to see quite different results sets depending on the
search engine and search query used. Organic results still play the major role
in the results pages, but different shortcuts are of some importance, too.
Regarding the frequency of certain host within the results sets, we find that
all search engines show Wikipedia results quite often, while other hosts shown
depend on the search engine used. Both Google and Yahoo prefer results from
their own offerings (such as YouTube or Yahoo Answers). Since we used the .com
interfaces of the search engines, results may not be valid for other
country-specific interfaces.
