Substitution analysis is a powerful tool to examine and forecast the substitution of one technology for another. In this case, the substitution is electronic media for print media in the reference library. The surrogate data that we have is that provided by Association of Research Libraries. It is not the complete world of expenditures on reference materials for libraries, but it is representative, at least of the big libraries. The data that ARL provides is a measure of expenditures. This is a useful surrogate for the number of units, the number of users or the amount of material, all potentially more direct measures of the substitution. However, sales figures are quite often used as they provide an aggregate way of indicating the impact of the new technology on the market.
It is also important to note that there are multiple substitutions going on in a cascade of change from print - CD, LAN and Internet, to just name a few. If data were available on this level of detail, a multiple substitution model could be created.
The Fisher-Pry substitution model is often used to analyze a substitution like electronic for print media in the reference library. The relationship between the fraction of total market taken by the new technology, f, is often given as:
f = 1 /(1 + c exp(-bt))
where t is time, and c and b are empirically determined coefficients. In this case b and c were determined from the data provided by Association of Reference Libraries for the years 1992 to 2004.
When these data are analyzed utilizing the Fisher-Pry method, the graph shown in Figure 1 results. It clearly indicates that the substitution of electronic for print is well underway in reference materials. The crossover point will occur in 2008 and 90% substitution will be achieved ten years later.
Figure 1. Data: http://www.arl.org/
Taking 1990 as the beginning of the substitution, and the middle projection, the time to 90% substitution by electronic media will take 28 years.
One of the interesting, and most insidious aspects of this type of substitution, when the substitution is taking place in a growing market, is that a large percentage of the substitution has taken place before the old technology sees two successive years of decreased revenue. This is the case here as well. Fifty percent of the total time to 90% substitution has elapsed before the print media have experienced two years decline, as shown in Figure 2.
There is an additional substitution going on and that is collaborative user generated content for traditional organized, hierarchical development and production. The reference industry is a pioneer in this substitution in Wikipedia. This is a substitution within the electronic reference resources, and unfortunately we have no data to indicate how this substitution is progressing. Revenue is not a good surrogate for this type of substitution as the results of the Wikipedia effort are available for free. The only possible measure would be the number of accesses or amount of time that people use Wikipedia versus other traditional reference resources. Wikipedia is certainly growing fast (Figure 3), in spite of professional criticism of the quality of the effort. Figure three indicates the growth in the number of English articles. The number of English articles is projected to be:
Figure 3. Source: Wikipedia
The transformation of the reference library has not been completed. There are many factors, trends and driving forces that could affect the future of the reference library. I think that the two most important trends affecting the future of the reference library, and by association, the reference publishing industry are: search engines vs. indexed collections, and proprietary vs. open content creation.
Search engines select information to be delivered to you based on your keywords matching them to the content of documents it searches, based on the algorithm of the search engine. It does not deliver the information that is "best" for the purpose of the researcher, as a reference librarian would, nor does it verify its authority, as indexed and abstracted peer reviewed articles/books/reports does. Most search engines will deliver documents that are current, are used frequently and are linked to my other documents (a type of authority measure). What search engines provide is quick, cheap access to over a billion web sites in the world. Given the high costs of the traditional system, and the rapid improvement of search engines, I see search engines providing a lot of the services now fulfilled by reference librarians, and the reference publishing industry.