  Web search engines have become the dominant tools for finding information on
the Internet. Due to their popularity, users apply them to a wide range of
search needs, from simple look-ups to rather complex information tasks. This
paper presents the results of a study to investigate the characteristics of
these complex information needs in the context of Web search engines. The aim
of the study is to find out more about (1) what makes complex search tasks
distinct from simple tasks and if it is possible to find simple measures for
describing their complexity, (2) if search success for a task can be predicted
by means of unique measures, and (3) if successful searchers show a different
behavior than unsuccessful ones. The study includes 60 people who carried out a
set of 12 search tasks with current commercial search engines. Their behavior
was logged with the Search-Logger tool. The results confirm that complex tasks
show significantly different characteristics than simple tasks. Yet it seems to
be difficult to distinguish successful from unsuccessful search behaviors. Good
searchers can be differentiated from bad searchers by means of measurable
parameters. The implications of these findings for search engine vendors are
discussed.
