\section*{Methods}
To investigate the historical and disciplinary effects of the \textit{h}-index, we calculate
individual researcher performance on a virtually complete
astronomy database of 814,505 refereed publications extracted from the
Smithsonian/NASA Astrophysics Data System
(\url{http://adsabs.harvard.edu/}) \cite{kurtz05a}. 
We focus on the careers of 11,036 astronomers with non ambiguous names, with a
publication record of over 20 refereed articles and a career span of
over 10 years, who are either currently active or have a career length
of at least 30 years which started on or after 1950. We define the
beginning of the career as the year of publication of an astronomer's
first refereed article. To begin, we compute the \textit{m}-quotient
on this cohort of astronomers and demonstrate that it is not 
constant over time and across sub-disciplines of astronomy.
Then, we propose a novel measure of research performance, the research
impact quotient (\textit{riq}). We compute \textit{riq} on the
same bibliographic corpus showing that this derived measure eliminates most historical
and disciplinary bias.
