Acceso usuarios
David I. Méndez Alcaraz, María Ángeles Alcaraz Ariza 
This article reports the findings of a diachronic study of acknowledgement practices in 300 randomly collected research papers published during three different periods (1998, 2004 and 2012) in the most prestigious American and European astrophysics journals written in English. In order to investigate the influence of these practices on authorship patterns, we analyzed the distribution over time of a series of quantitative variables (number, length and types of acknowledgements, mean number of words/number of acknowledgements per research paper and mean number of acknowledgements/number of authors per research paper, number of named and unnamed acknowledgees, number of identified and anonymous referees, and number of emotionally charged-words). Comparisons between periods were carried out and Student’s t-tests were applied to the quantitative results. Our main findings show that acknowledgements are very common in astrophysics since they are present in 96% of the whole corpus. Financial, mainly public, and instrumental supports are the most frequently acknowledged categories. The number and length of acknowledgements and the mean number of words/number of acknowledgements per research paper grow over time. Financial, instrumental and conceptual assistance, unnamed individuals and anonymous referees increase over time, whereas moral, editorial and unclassified supports, named individuals and identified referees, and emotionally-charged words decline. If we focus on each journal publication context, we can observe that the research papers published in the American journals include more and longer acknowledgements, with a higher mean number of acknowledgements per author, more financial and instrumental supports, and a lower percentage of emotionally-charged words, whereas the European journals contain more conceptual and editorial supports. All these data can be understood in the frame of growing scientific professionalism, while a detailed cross-journal analysis may occasionally suggest honorary/guest/gift authorship.
