'Bad' distributions of good data: unusual statistics of structural databases.

Distributions of data taken from crystal structure databases, display unusual statistical properties like non-Gaussian shape, polymodality, and heavy tails. These features, typical for statistics of numerical data in social systems, appear in bigger sets (from hundreds to many thousand points) of database-originated parameters. The non-classic statistics of physical data collected through many years reflects a strong impact of social factors (financial support, exchange of information, competition, etc.) on a research activity. The values of some definite structural parameter, determined (and deposited to a database) by different authors, generally are neither independent nor random; their handling by common statistical tools may result in incorrect conclusions and wrong predictions. These statements are illustrated by several sets of reliable structural data whose statistics looks 'bad,' or inconclusive, in contemporary structural chemistry. [ABSTRACT FROM AUTHOR]