CSA3200: Adaptive Hypertext Systems

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CSA3200Adaptive Hypertext Systems
Lecture 10 Evaluation Methods

• Dr. Christopher Staff
• Department of Intelligent Computer Systems
• University of Malta

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Aims and Objectives

• Background to evaluation methods in user-adaptive
  systems
• Brief overviews of the evaluation of IR, QA, User
  Modelling, Recommender Systems, Intelligent
  Tutoring Systems, Adaptive Hypertext Systems

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Background to Evaluation Methods

• Systems need to be evaluated to demonstrate
  (prove) that the hypothesis on which they are
  based is correct
• In IR, we need to know that the system is
  retrieving all and only relevant documents for
  the given query

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Background to Evaluation Methods

• In QA, we need to know the correct answer to
  questions, and measure performance
• In User Modelling, we need to determine that the
  model is an accurate reflection of information
  needed to adapt to the user
• In Recommender Systems, we need to associate user
  preferences either with other similar users, or
  with product features

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Background to Evaluation Methods

• In Intelligent Tutoring Systems we need to know
  that learning through an ITS is beneficial or at
  least not (too) harmful
• In Adaptive Hypertext Systems, we need to measure
  the systems ability to automatically represent
  user interests, to direct the user to relevant
  information, and to present the information in
  the best way

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Measuring Performance

• Information Retrieval
• Recall and Precision (overall, and also at top-n)
• Question Answering
• Mean Reciprocal Rank

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Measuring Performance

• User Modelling
• Precision and Recall if user is given all and
  only relevant info, or if system behaves exactly
  as user needs, then model is probably correct
• Accuracy and predicted probability to predict a
  users actions, location, or goals
• Utility the benefit derived from using system

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Measuring Performance

• Recommender Systems
• Content-based may be evaluated using precision
  and recall
• Collaborative is harder to evaluate, because it
  depends on other users the system knows about
• Quality of individual item prediction
• Precision and Recall at top-n

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Measuring Performance

• Intelligent Tutoring Systems
• Ideally, being able to show that student can
  learn more efficiently using ITS than without
• Usually, show that no harm is done
• Then, releasing the tutor and enabling
  self-paced learning becomes a huge advantage
• Difficult to evaluate
• Cannot compare same student with and without ITS
• Students who volunteer are usually very motivated

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Measuring Performance

• Adaptive Hypertext Systems
• Can mix UM, IR, RS (content-based) methods of
  evaluation
• Use empirical approach
• Different sets of users solve same task, one
  group with adaptivity, the other without
• How to choose participants?

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Evaluation Methods IR

• IR systems performance is normally measured
  using precision and recall
• Precision percentage of retrieved documents that
  are relevant
• Recall percentage of relevant documents that are
  retrieved
• Who decides which documents are relevant?

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Evaluation Methods IR

• Query Relevance Judgements
• For each test query, the document collection is
  divided into two sets relevant and non-relevant
• Systems are compared using precision and recall
• In early collections, humans would classify
  documents (p3-cleverdon.pdf)
• Cranfield collection 1400 documents/221 queries
• CACM 3204 documents/50 queries

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Evaluation Methods IR

• Do humans always agree on relevance judgements?
• No can vary considerably (mizzaro96relevance.pdf)
  
• So only use documents on which there is full
  agreement

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Evaluation Methods IR

• Text REtrieval Conference (TREC)
  (http//trec.nist.gov)
• Runs competitions every year
• QRels and document collection made available in a
  number of tracks (e.g., ad hoc, routing, question
  answering, cross-language, interactive, Web,
  terabyte, ...)

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Evaluation Methods IR

• What happens when collection grows?
• E.g., Web track has 1GB of data! Also have
  Terabyte track
• Pooling
• Give different systems same document collection
  to index and queries
• Take the top-n retrieved documents from each
• Documents that are present in all retrieved sets
  are relevant, others not OR
• Assessors judge the relevance of unique documents
  in the pool

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Evaluation Methods IR

• Advantages
• Possible to compare system performance
• Relatively cheap
• QRels and document collection can be purchased
  for moderate price rather than organising
  expensive user trials
• Can use standard IR systems (e.g., SMART) and
  build another layer on top, or build new IR model
• Automatic and Repeatable

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Evaluation Methods IR

• Common criticisms
• Judgements are subjective
• Same assessor may change judgement at different
  times!
• But doesnt effect ranking
• Judgements are binary
• Some relevant documents are missed by pooling
  (QRels are incomplete)
• Doesnt effect system performance

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Evaluation Methods IR

• Common criticisms (contd.)
• Queries are too long
• Queries under test conditions can have several
  hundred terms
• Average Web query length 2.35 terms
  (p5-jansen.pdf)

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Evaluation Methods IR

• In massive document collections there may be
  hundreds, thousands, or even millions of relevant
  documents
• Must all of them be retrieved?
• Measure precision at top-5, 10, 20, 50, 100, 500
  and take weighted average over results (Mean
  Average Precision)

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The E-Measure

• Combine Precision and Recall into
• one number (Effectiveness Measure)
• (http//www.dcs.gla.ac.uk/Keith/Chapter.7/Ch.7.htm
  l)

P precision R recall b measure of relative
importance of P or R E.g, b 0.5 means user is
twice as interested in precision as recall
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Evaluation Methods QA

• The aim in Question Answering is not to ensure
  that the overwhelming majority of relevant
  documents are retrieved, but to return an
  accurate answer
• Precision and recall are not accurate enough
• Usual measure is Mean Reciprocal Rank

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Evaluation Methods QA

• MRR measures the average rank of the first
  correct answer for each query (1/rank, or 0 if
  correct answer is not in top-5)
• Ideally, the first correct answer is put into
  rank 1

qa_report.pdf
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Evaluation Methods UM

• Information Retrieval evaluation has matured to
  the extent that it is very unusual to find an
  academic publication without a standard approach
  to evaluation
• On the other hand, up to 2001, only one-third of
  user models presented in UMUAI (user modeling and
  user-adapted interaction) had been evaluated and
  most of those were ITS related (see later)

p181-chin.pdf
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Evaluation Methods UM

• Unlike IR systems, it is difficult to evaluate
  UMs automatically
• Unless they are stereotypes/course-grained
  classification systems
• So they tend to need to be evaluated empirically
• User studies
• Want to measure how well participants do with and
  without a UM supporting their task

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Evaluation Methods UM

• Difficulties/problems include
• Ensuring a large enough number of participants to
  make results statistically meaningful
• Catering for participants improving during rounds
• Failure to use a control group
• Ensuring that nothing happens to modify
  participants behaviour (e.g., thinking aloud)

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Evaluation Methods UM

• Difficulties/problems (contd.)
• Biasing the results
• Not using blind-/double-blind testing when needed
• ...

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Evaluation Methods UM

• Proposed reporting standards
• No., source, and relevant background of
  participants
• independent, dependent and covariant variables
• analysis method
• post-hoc probabilities
• raw data (in the paper, or on-line via WWW)
• effect size and power (at least 0.8)

p181-chin.pdf
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Evaluation Methods RS

• Recommender Systems
• Two types of recommender system
• Content-based
• Collaborative
• Both (tend to) use VSM to plot users/ product
  features into n-dimensional space

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Evaluation Methods RS

• If we know the correct recommendations to make
  to a user with a specific profile, then we can
  use Precision, Recall, EMeasure, Fmeasure, Mean
  Average Precision, MRR, etc.

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Evaluation Methods ITS

• Intelligent Tutoring Systems
• Evaluation to demonstrate that learning through
  ITS is at least as effective as traditional
  learning
• Cost benefit of freeing up tutor, and permitting
  self-paced learning
• Show at a minimum that student is not harmed at
  all or is minimally harmed

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Evaluation Methods ITS

• Difficult to prove that individual student
  learns better/same/worse with ITS than without
• Cannot make student unlearn material in between
  experiments!
• Attempt to use statistically significant number
  of students, to show probable overall effect

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Evaluation Methods ITS

• Usually suffers from same problems as evaluating
  UMs, and ubiquitous multimedia systems
• Students volunteer to evaluate ITSs
• So are more likely to be motivated and so perform
  better
• Novelty of system is also a motivator
• Too many variables that are difficult to cater for

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Evaluation Methods ITS

• However, usually empirical evaluation is
  performed
• Volunteers work with system
• Pass rates, retention rates, etc., may be
  compared to conventional learning environment
  (quantitative analysis)
• Volunteers asked for feedback about, e.g.,
  usability (qualitative analysis)

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Evaluation Methods ITS

• Frequently, students are split into groups
  (control and test) and performance measured
  against each other
• Control is usually ITS without the I - students
  must find their own way through learning material
• However, this is difficult to assess, because
  performance of control group may be worse than
  traditional learning!

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Evaluation Methods ITS

• Learner achievement metric (Muntean, 2004)
• How much has student learnt from ITS?
• Compare pre-learning knowledge to post-learning
  knowledge
• Can compare different systems (as long as they
  use same learning material), but with different
  users so same problem as before

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Evaluation Methods AHS

• Adaptive Hypertext Systems
• There are currently no standard metrics for
  evaluating AHSs
• Best practices are taken from fields like ITS,
  IR, and UM and applied to AHS
• Typical evaluation is experiences of using
  system with and without adaptive features

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Evaluation Methods AHS

• If a test collection existed for AHS (like TREC)
  what might it look like?
• Descriptions of user models relevance
  judgements for relevant links, relevant
  documents, relevant presentation styles
• Would we need a standard open user model
  description? Are all user models capturing the
  same information about the user?

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Evaluation Methods AHS

• What about following paths through hyperspace to
  pre-specified points and then having the sets of
  judgements?
• Currently, adaptive hypertext systems appear to
  be performing very different tasks, but even if
  we take just one of the two things that can be
  adapted (e.g., links), it appears to be beyond
  our current ability to agree on how adapting
  links should be evaluated, mainly due to UM!

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Evaluation Methods AHS

• HyperContext (HCT) (HCTCh8.pdf)
• HCT builds a short-term user model as a user
  navigates through hyperspace
• We evaluated HCTs ability to make See Also
  recommendations
• Ideally, we would have had hyperspace with
  independent relevance judgements a particular
  points in path of traversal

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Evaluation Methods AHS

• Instead, we used two mechanisms for deriving UM
  (one using interpretation, the other using whole
  document)
• After 5 link traversals we automatically
  generated a query from each user model, submitted
  it to search engine and found a relevant
  interpretation/document respectively

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Evaluation Methods AHS

• Users asked to read all documents in the path and
  then give relevance judgement for each See Also
  recommendation
• Recommendations shown in random order
• Users didnt know which was HCT recommended and
  which was not
• Assumed that if user considered doc to be
  relevant, then UM is accurate

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Evaluation Methods AHS

• Not really enough participants to make strong
  claims about HCT approach to AH
• Not really significant differences in RJs between
  different ways of deriving UM (although both
  performed reasonably well!)
• However, significant findings if reading time is
  indication of skim-/deep-reading!

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Evaluation Methods AHS

• Should users have been shown both documents?
• Could reading two documents, instead of just one,
  have effected judgement of doc read second?
• Were users disaffected because it wasnt a task
  that they needed to perform?

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Evaluation Methods AHS

• Ideally, systems are tested in real world
  conditions in which evaluators are performing
  tasks
• Normally, experimental set-ups require users to
  perform artificial tasks, and it is difficult to
  measure performance because relevance is
  subjective!

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Evaluation Methods AHS

• This is one of the criticisms of the TREC
  collections, but it does allow systems to be
  compared - even if the story is completely
  different once the system is in real use
• Building a robust enough system for use in the
  real world is expensive
• But then, so is conducting lab based experiments

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Modular Evaluation of AUIs

• Adaptive User Interfaces, or User-Adaptive
  Systems
• Difficult to evaluate monolithic systems
• So break up UASs into modules that can be
  evaluated separately

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Modular Evaluation of AUIs

• Paramythis, et. al. recommend
• identifying the evaluation objects - that can
  be evaluated separately and in combination
• presenting the evaluation purpose - the
  rationale for the modules and criteria for their
  evaluation
• identifying the evaluation process - methods
  and techniques for evaluating modules during the
  AUI life cycle

paramythis.pdf
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Modular Evaluation of AUIs
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Modular Evaluation of AUIs