Page 105 - DLIS405_INFORMATION_STORAGE_AND_RETRIEVAL
P. 105
Information Storage and Retrieval
Notes
In binary classification, recall is called sensitivity. So it can be looked at as the
probability that a relevant document is retrieved by the query.
It is trivial to achieve recall of 100% by returning all documents in response to any query. Therefore,
recall alone is not enough but one needs to measure the number of non-relevant documents also,
for example by computing the precision.
Precision and recall are the basic measures used in evaluating search strategies
As shown in the first two figures on the left, these measures assume:
1. There is a set of records in the database which is relevant to the search topic.
2. Records are assumed to be either relevant or irrelevant (these measures do not allow for
degrees of relevancy).
Figure 10.1
The set of
items
retrieved
The set of relevant
items in the database
Figure 10.2
Irrelevant
items-
retrieved
Relevant items-retrived
Relevant items-not retrived
3. The actual retrieval set may not perfectly match the set of relevant records.
RECALL is the ratio of the number of relevant records retrieved to the total number of relevant
records in the database. It is usually expressed as a percentage.
100 LOVELY PROFESSIONAL UNIVERSITY
