© Tefko Saracevic1 Search strategy & tactics Governed by effectiveness&feedback

© Tefko Saracevic2 Some definitions Search statement (query): –set of search terms with logical connectors and attributes - file and system dependent Search strategy (big picture): –overall approach to searching of a question  selection of systems, files, search statements & tactics, sequence, output formats; cost, time aspects

© Tefko Saracevic3 Some definitions (cont.) Search tactics (action choices): –choices & variations in search statements  terms, connectors, attributes Move : –modifications of search strategies or tactics that are aimed at improving the results Cycle (particularly applicable to systems such as DIALOG): –set of commands from start (begin) to viewing (type) results, or from a viewing to a viewing command

© Tefko Saracevic4 Some definitions (cont.) Effectiveness : –performance as to objectives  to what degree did a search accomplish what desired?  how well done in terms of relevance? Efficiency : –performance as to costs  at what cost and/or effort, time? Both KEY concepts & criteria for selection of strategy, tactics & evaluation

© Tefko Saracevic5 Effectiveness criteria Search tactics chosen & changed following some criteria of accomplishment, such as: –none - no thought given –relevance (very often) –magnitude (also very often) –output attributes –topic/strategy Tactics altered interactively –role & types of feedback Knowing what tactics may produce what results key to professional searcher

© Tefko Saracevic6 Relevance: key concept in IR Attribute/criterion reflecting effectiveness of exchange of inf. between people (users) & IR systems in communication contacts, based on valuation by people Some attributes: –in IR - user dependent –multidimensional or faceted –dynamic –measurable - somewhat –intuitively well understood

© Tefko Saracevic7 Types of relevance Several types considered: –Systems or algorithmic relevance  relation between between a query as entered and objects in the file of a system as retrieved or failed to be retrieved by a given procedure or algorithm. Comparative effectiveness. –Topical or subject relevance:  relation between topic in the query & topic covered by the retrieved objects, or objects in the file(s) of the system, or even in existence; Aboutness..

© Tefko Saracevic8 Types of relevance (cont.) –Cognitive relevance or pertinence:  relation between state of knowledge & cognitive inf. need of a user and the objects provided or in the file(s). Informativeness, novelty... – Motivational or affective relevance  relation between intents, goals & motivations of a user & objects retrieved by a system or in the file, or even in existence. Satisfaction... –Situational relevance or utility:  relation between the task or problem-at-hand. and the objects retrieved (or in the files). Relates to usefulness in decision-making, reduction of uncertainty...

© Tefko Saracevic9 Effectiveness measures Precision: – probability that given that an object is retrieved it is relevant, or the ratio of relevant items retrieved to all items retrieved Recall: – probability that given that an object is relevant it is retrieved, or the ratio of relevant items retrieved to all relevant items in a file Precision easy to establish, recall is not  union of retrievals as a “trick” to establish recall

© Tefko Saracevic10 Precision = a a + b Recall = a a + c Calculation High precision = maximize a, minimize b High recall = maximize a, minimize c

© Tefko Saracevic11 Interpretation: PRECISION Precision= percent of relevant stuff you have in your answer –or conversely percent of junk –high precision = most stuff relevant –low precision = a lot of junk Some users demand high precision –do not want to wade through much stuff –but it comes at a price: relevant stuff may be missed  tradeoff

© Tefko Saracevic12 A file may have a lot of relevant stuff Recall = percent of that relevant stuff in the file that you retrieved –conversely percent of stuff you missed –high recall = you missed little –low recall = you missed a lot Some users demand high recall (e.g. PhD students doing dissertation) –want to make sure that important stuff is not missed –but will have to pay a price of wading through a lot of junk  tradeoff Interpretation: RECALL

© Tefko Saracevic13 Precision-recall trade-off USUALLY: precision & recall are inversely related –higher recall usually lower precision & vice versa 100 % 0 Ideal Usual Improvements Precision Recall

© Tefko Saracevic14 Interpretation: TRADE-OFF It is like in life, usually: – you get some lose some Usually, but not always  keep in mind these are probabilities –when you have high precision most stuff you got is relevant or on the target but you missed stuff that is also relevant – it was left behind –when you have high recall you did not miss much but you got also a lot of junk - wading through it You use different tactics for high recall from those for high precision

© Tefko Saracevic15 Search tactics What variations possible? –several ‘things’ in a query can be selected or changed that affect effectiveness –each variation has consequence in output  if I do X then Y will happen 1. LOGIC –choice of connectors among terms (AND, OR, NOT, W …) 2. SCOPE –no. of terms linked - ANDs (A AND B vs A AND B AND C)

© Tefko Saracevic16 Search tactics (cont.) 3.EXHAUSTIVITY –for each concept no. of related terms - OR connections (A OR B vs. A OR B OR C) 4. TERM SPECIFICITY –for each concept level in hierarchy (broader vs narrower terms) 5. SEARCHABLE FIELDS –choice for text terms & non-text attributes  e.g. titles only, limit as to years 6. FILE OR SYSTEM SPECIFIC CAPABILITIES –e.g. ranking, sorting

© Tefko Saracevic17 Effectiveness “laws” SCOPE - adding more ANDs EXHAUSTIVITY - adding more more ORs USE OF NOTs - adding more NOTs BROAD TERM USE –low specificity Output size: down Recall: down Precision: up Output size: up Recall: up Precision: down Output size down Recall: down Precision: up Output size: up Recall: up Precision: down Output size: down Recall: down Precision: up PHRASE USE - high specificity

© Tefko Saracevic18 Tactics: What to do? To increase precision: –use precision devices To increase recall: –use recall devices Each will also affect magnitude of output With experience use of these devices will become will become second nature

© Tefko Saracevic19 Recall, precision devices BROADENING higher recall: Fewer ANDs More ORs Fewer NOTs More free text Fewer controlled More synonyms Broader terms Less specific More truncation Fewer qualifiers Fewer limits Citation growing NARROWING - higher precision: More ANDs Fewer ORs More NOTs Less free text More controlled Less synonyms Narrower terms More specific Less truncation More qualifiers More limits Building blocks

© Tefko Saracevic20 Other tactics Citation growing: –find a relevant document –look for documents cited in –look for documents citing it –repeat on newly found relevant documents Building blocks –find documents with term A –review – add term B & so on Using different feedbacks –a most important tool

© Tefko Saracevic21 Feedback in searching Any feedback implies loops –a completion of a process provides information for modification, if any, for the next process –information from output is used to change previous or create new input In searching: –some information taken from output of a search is used to do something with next query (search statement)  examine what you got to decide what to do next in searching –a basic tactic in searching Several feedback types used in searching –each used for different decisions

© Tefko Saracevic22 Feedback types Content relevance feedback –judge relevance of items retrieved –make decision what to do next  switch files, change exhaustivity … Term relevance feedback –find relevant documents –examine what other terms used in those documents –search using additional terms  also called query modification & in some systems done automatically Magnitude feedback –on the basis of size of output make tactical decisions  often the size so big that documents are not examined but next search done to limit size

© Tefko Saracevic23 Feedback types (cont.) Tactical review feedback –after a number of queries (search statements) in the same search review tactics as to getting desired outputs  review terms, logic, limits … –change tactics accordingly Strategic review feedback –after a while (or after consultation with user) review the “big” picture on what searched and how  sources, terms, relevant documents, need satisfaction, changes in question, query … –do next searches accordingly –used in reiterative searching There is a difference between reviewing strategy & tactics –but they can be combined

© Tefko Saracevic24 Bates Berry-picking model of searching “…moving through many actions towards a general goal of satisfactory completion of research related to information need.” –query is shifting (continually)  as search progresses queries are changing  different tactics are used –searcher (user) may move through a variety of sources  new files, resources may be used  strategy may change

© Tefko Saracevic25 Berry-picking … –new information may provide new ideas, new directions feedback is used in various ways –question is not satisfied by a single set of answers, but by a series of selections & bits of information found along the way  results may vary & may have to be provided in appropriate ways & means