9. The NSFNET backbone was originally the core of the Internet, and thus much of the total Internet traffic passed through it, making useful measurement of total Internet traffic possible. When this backbone was replaced by a new architecture, data on total traffic became harder to acquire. Also, the architecture of the backbone had been designed to allow more measurements than are now possible with the off-the-shelf router components that were used post-NSFNET, in order to satisfy deliverables of traffic measurement in the agreement with NSF.
10. Web advertising is one area where an effort has been made to develop useful definitions of access and use (Novak and Hoffman, 1997).
11. For several years in the early 1990s Brian Reid, an employee of the Digital Equipment Corporation, collected and posted on the Internet data on Usenet groups. Each month he used a sampling plan to report estimates of Usenet readership and message traffic for all Usenet groups. Researchers were able to use Reid's data to track growth in overall group membership over time, track the relative popularity of different groups at any one point in time, or identify groups worthy of further study (e.g., Sproull and Faraj, 1995). Reid stopped collecting and reporting Usenet data in June 1995.
12. Reid's study of Usenet traffic is a case in point. One reason Reid stopped collecting Usenet data was that its relevance declined when the World Wide Web was invented and the ratio of quality material to junk declined markedly. Another reason was the evolution of the way Usenet data was distributed, which made the study's measurement techniques increasingly statistically meaningless. However, the ultimate reason for ending the study was not technological, but rather was related to the threat of legal challenges over privacy issues surrounding collection, analysis, and publication of the Usenet data (personal communication, Brian Reid, Digital Equipment Corporation, 1998).
13. This work replicated findings by Hesse et al. (1993) derived from analysis of electronic survey data.
14. GenBank, an annotated collection of publicly available DNA sequences, is part of the International Nucleotide Sequence Database Collaboration, which comprises the DNA Data Bank of Japan, the European Molecular Biology Laboratory data library, and GenBank. More information on GenBank may be found online at ‹http://www.ncbi.nlm.nih.gov/Web/Genbank/index.html›.