lecture15-webchar-handout-6-per

Precisionvsrecall onthewebrecallseldommapers

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Unformatted text preview: o
that
page
(~25%
/
15%)
 Web spider   Transac(onal
–
want
to
do
something
(web‐mediated)
(~35%
/
20%)
   Access
a

service
 Search Indexer   Downloads

   Shop
   Gray
areas
   Find
a
good
hub
   Exploratory
search
“see
what’s
there”

 The Web Indexes 5
 Ad indexes 6
 1 Introduc)on to Informa)on Retrieval Introduc)on to Informa)on Retrieval How
far
do
people
look
for
results?
 Users’
empirical
evalua)on
of
results
   Quality
of
pages
varies
widely
   Relevance
is
not
enough
   Other
desirable
quali)es
(non
IR!!)
   Content:
Trustworthy,
diverse,
non‐duplicated,
well
maintained
   Web
readability:
display
correctly
&
fast
   No
annoyances:
pop‐ups,
etc.
   Precision
vs.
recall
   On
the
web,
recall
seldom
mapers
   What
mapers
   Precision
at
1?
Precision
above
the
fold?
   Comprehensiveness
–
must
be
able
to
deal
with
obscure
queries
   Recall
mapers
when
the
number
of
matches
is
very
small
   User
percep)ons
may
be
unscien)fic,
but
are
significant
 over
a
large
aggregate
 (Source: iprospect.com WhitePaper_2006_SearchEngineUserBehavior.pdf) 7
 Introduc)on to Informa)on Retrieval Sec. 19.2 Introduc)on to Informa)on Retrieval The
Web
document
collec)on
 Users’
empirical
evalua)on
of
engines
           8
 Relevance
and
validity
of
results
 UI
–
Simple,
no
cluper,
error
tolerant
 Trust
–
Results
are
objec)ve
 Coverage
of
topics
for
polysemic
queries
 Pre/Post
process
tools
provided
   Mi)gate
user
errors
(auto
spell
check,
sea...
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