The case against citation metrics

This year I am on a committee that looks at funding applications from all areas of science. Inevitably, this will lead to problematic comparisons of the track records of mathematicians versus physicists versus biologists. The quick, lazy, and unjustified recourse is to start invoking impact factors and publications in luxury journals.

There is a very thorough and helpful report Citation Statistics from the International Mathematical Union that clearly shows how problematic citation metrics are.
Of particular interest is the graph below.

Note that mathematicians are cited three times less than physicists and six times less than life scientists.

Aside: I am not clear what the distinction is between life sciences and biological sciences. Is the latter more oriented to humans [e.g. medicine] and the latter plants and animals?

This report is cited in the San Francisco Declaration on Research Assessment, initiated by biologists, that is attracting significant interest and mentioned by Carl Caves on High Impact Factor Syndrome.