Quality matters—and the choice of indicator matters too

EDITOR—Results of the analysis by Joseph add new data and a remarkable twist to existing knowledge on weaknesses in the accuracy of the data that the Institute for Scientific Information (now part of the Thomson company) uses.1 Although the institute has long struggled to avoid mistakes, the vast amount of data needed to create its products emphasises the importance of more stringent quality checks.2 These controls are impossible to perform by users of the institute's indices and databases, since most users do not have access to the original, raw data—access, for example, to data on which articles were counted to be part of the denominator of the bibliographical “impact factor”.2