# Relatedness Measures

## Lesk

The Lesk measure works by finding overlaps in the extended definitions
of the two concepts. The relatedness score is the sum of the squares of
the overlap lengths. For example, a single word overlap results in a
score of 1. Two single word overlaps results in a score of 2. A two
word overlap (i.e., two consecutive words) results in a score of 4. A
three word overlap results in a score of 9.

## Vector

The vector measure works by forming second-order
co-occurrence vectors from the UMLS extended definitions of concepts.
The relatedness of two concepts is determined as the cosine of the
angle between their vectors.