The measurement of the effect on citation inequality of differences in citation practices across scientific fields.

This paper has two aims: (i) to introduce a novel method for measuring which part of overall citation inequality can be attributed to differences in citation practices across scientific fields, and (ii) to implement an empirical strategy for making meaningful comparisons between the number of citations received by articles in 22 broad fields. The number of citations received by any article is seen as a function of the article's scientific influence, and the field to which it belongs. A key assumption is that articles in the same quantile of any field citation distribution have the same degree of citation impact in their respective field. Using a dataset of 4.4 million articles published in 1998-2003 with a five-year citation window, we estimate that differences in citation practices between the 22 fields account for 14% of overall citation inequality. Our empirical strategy is based on the strong similarities found in the behavior of citation distributions. We obtain three main results. Firstly, we estimate a set of average-based indicators, called exchange rates, to express the citations received by any article in a large interval in terms of the citations received in a reference situation. Secondly, using our exchange rates as normalization factors of the raw citation data reduces the effect of differences in citation practices to, approximately, 2% of overall citation inequality in the normalized citation distributions. Thirdly, we provide an empirical explanation of why the usual normalization procedure based on the fields' mean citation rates is found to be equally successful.

The citation merit of scientific publications.

We propose a new method to assess the merit of any set of scientific papers in a given field based on the citations they receive. Given a field and a citation impact indicator, such as the mean citation or the [Formula: see text]-index, the merit of a given set of [Formula: see text] articles is identified with the probability that a randomly drawn set of [Formula: see text] articles from a given pool of articles in that field has a lower citation impact according to the indicator in question. The method allows for comparisons between sets of articles of different sizes and fields. Using a dataset acquired from Thomson Scientific that contains the articles published in the periodical literature in the period 1998-2007, we show that the novel approach yields rankings of research units different from those obtained by a direct application of the mean citation or the [Formula: see text]-index.

Interacción de cepas verocitotóxicas de Escherichia coli y rotavirus en un brote de diarrea en becerros / Interaction of Escherichia coli verocytotoxin strains and rotavirus in an outbreak of calves diarrhoea

Se estudió un brote de diarrea hemorrágica en becerros de 1 a 20 días de edad, de curso agudo, con edema gastrointestinal, signos nerviosos y sin respuesta al tratamiento con antibióticos. Se realizaron estudios parasitológicos, bacteriológicos e identificación de rotavirus. Se determinó en las cepas de Escherichia coli aisladas la capacidad de producir citotoxinas sobre células vero. El 63.7 por ciento de las cepas aisladas de E.coli resultaron verocitotóxicas (productoras de toxina vero o de toxina shiga, Stx), estas cepas se aislaron del 86.5 por ciento de los animales afectados. En 24 por ciento de estos animales se determinó la presencia de rotavirus mediante electroforesis en PAGE. Se encontraron variaciones en la movilidad electroforética de las bandas. Todos los casos con identificación de rotavirus correspondieron con la presencia de cepas de Escherichia coli productoras de toxina siga (STEC) en el intestino. El porcentaje de riesgo calculado, de presentar infección con rotavirus atribuible a la infección con E.coli STX, fue de 100, no existió, en cambio, riesgo de presentar cepas STX si se presentaba una infección primaria con rotavirus. Los datos sugieren que las cepas citotóxicas son agentes primarios de infección y toxemia neonatal en bovinos; a la vez, se refuerza el probable papel de los bovinos como reservorios de cepas citotóxicas que afectan al humano y determinan el síndrome urémico hemolítico.