(ă-trish'ŏn )

[L. attritio, a rubbing against]

1. The act of wearing away by friction or rubbing.
2. Any friction that breaks the skin.
3. The process of wearing away, as of teeth, in the course of normal use.
4. In research, the progressive loss of study subjects with each passing year because of, e.g., relocation, lack of interest, failure of outreach, or death.

attritional,

(ă-trish'ŏ-năl )