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“4137X˙CH02˙Akerkar” — 2007/9/20 — 10:12 — page 63 — #45
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2.4 Evaluation of Retrieval Performance 63
R = Relevant documents A = Retrieved documents
Figure 2.42 Illustration of precision and recall measures
Here, |R|, |A|, and|R ∩ A| are the cardinalities (or size) of the sets R, A, and R ∩ A. Precision
is a measure of the accuracy of our retrieval. Higher precision implies that the probability
of a retrieved document being relevant is high. The recall, on the other hand, tells us what
percentage of documents was actually retrieved. If the recall value is closer to 1.0, we have
most of the relevant documents from the collection. Usually precision ...