1. A computer-implemented method for rapidly identifying and ranking relevant documents, said method comprising: receiving, by a computer system comprising one or more computing devices, a first set of identification information identifying one or more input documents for which relevant output documents are sought, wherein the one or more input documents are identified from a body of data, said body of data comprising identification information identifying multiple millions of citationally related documents; identifying, by said computer system, a second set of identification information identifying one or more output documents from said body of data that are citationally related to said one or more input documents through one or more direct or indirect citations; determining, by said computer system, a first numerical score that statistically correlates to a probability that a direct citation exists between each input document relative to each citationally related output document, said first numerical score being determined based at least in part on how many indirect citations exist between each input document and each output document and, for each indirect citation, how many citation links separate each input document from each output document; determining, by said computer system, a second numerical score that statistically correlates to a probability that a direct citation exists between any input document relative to each output document, said second numerical score being determined based at least in part on said first numerical score; ranking, by said computer system, said one or more output documents in accordance with said second numerical score; and displaying, by said computer system, a third set of identification information identifying a selected number of said one or more output documents selected or ranked in accordance with said second numerical score.