Stockholm University Library expressly conducts work with demand-driven acquisition and holdings. As a part of this, the library has in recent years made use of what are known as PDA and EBS models for purchasing e-books. 

“Users are involved in driving acquisition to a greater extent than in the past. They do this, among other things, by submitting purchase proposals on an order form on the library's website. But users also drive acquisition indirectly through their usage of our media resources. Media resources that are not used are terminated and we can resume them should a new need arise. Another example of users indirectly influencing acquisition through their usage is these very PDA and EBS models,” says Frida Jacobson, who has served as project manager for the working group that analysed the models.  


EBS and PDA as purchasing models

Put simply, the models mean that the library for a certain period of time gives users access to a large number of books via e-book platforms that are integrated with the rest of the library's range in the library catalogue. The e-book platforms are linked to one of the different purchasing models; PDA (Patron-Driven Acquisition) or EBS (Evidence-Based Selection). The agreements and an upfront payment give the library access to a great quantity of e-books for a certain period of time. In the EBS model, the library at the end of the agreement period manually selects the e-books that have been used the most, within the limits of the sum paid upfront. In the PDA model, purchases are generated automatically on the platform, based on user activities such as printing, downloading or browsing. This means that at the end of an agreement period the library owns some of the books on the e-book platform. 

One advantage of these purchasing models is that the library can give users access to more books than could otherwise be purchased within the acquisition budget. The work input for librarians working with acquisitions should also decrease, compared with their manually purchasing one book at a time when requested via the library's order form. Some questions that arise, however, are if one purchasing model is more advantageous than others, and if the library has invested in e-book platforms that generated highly used content in order to optimise the benefits.   

More titles or more user restrictions?

The work input for acquisitions librarians to manage the various models has varied, but the evaluation finds that PDA models from e-book suppliers (aggregators) have been more labour-intensive than EBS models from publishers. 

One advantage of a PDA from an aggregator is that the library can provide access to a great quantity of titles, some of which are from smaller publishers. But a disadvantage is that the books are subject to user restrictions. A restriction might involve limiting the number of simultaneous users to a maximum of one at a time, or limiting the number of pages the user can print from the e-book. One advantage of EBS models from publishers is that they do not have any user restrictions, but the disadvantage is that they provide access to relatively fewer titles as they only have titles from their own publisher. 

Humanities popular with users

The analysis of usage statistics within the ten models shows a clear trend that social sciences and humanities are popular areas. The most recently published titles have also been used the most. Usage is greatest for titles published in 2010-2015, followed by titles published in 2005-2009. This can provide guidance on which future e-book packages the library should invest in.

The format of e-books

The format of e-books has differed between the various e-book platforms. One platform had videos as a format, that is, the platform did not contain traditional e-books but instead had video collections. Five platforms had e-books in PDF format and four had the format PDF or ePub. In one of the e-book platforms which had both PDF and ePub, it was only newer titles from 2014 that were in ePub format.

Is then the format of significance to the user? The format can be of significance to user experience. Accessibility for the user might depend on the format but also on several other factors. In the present investigation, however, the library did not focus on analysing the significance of the format in particular, but found that this differed from platform to platform. 

What is the cost per book?

The average price per book at the time of purchase has varied between the compared models and differs by more than 240 per cent between the lowest average price and the highest average price – from SEK 755 to SEK 1,837. There was also great variation in the number of downloads, i.e. uses, made before a book was purchased. 

The cost per book also needs to be placed in relation to how much a book is used. A higher average price per book might be justified if its usage is high, as this reduces the price per use. For four of the analysed e-book platforms, Stockholm University Library has had agreements long enough to monitor the usage of purchased titles for several years. For three of four models, more than half of the purchased titles continued to be used in subsequent periods. For one of the models, a full 68 per cent of the purchased titles continued to be one year after the time of purchase. For example, the cost per used chapter for the titles the library purchased from a publisher in period 1, i.e. at the time of purchase, was SEK 181, but four years later the cost per use had fallen to SEK 52.

Why has Stockholm University Library carried out this investigation?

“It is important that we evaluate our resources to maximise the benefits and that we take the time to reflect on our purchasing processes. The analysis of the different models has provided us with knowledge for our library's work with acquisitions. Besides this, such an in-depth study of the usage statistics has given us additional insights into user behaviour,” says Mia Wahlberg, head of the library's Media Department, which works with acquisitions.

Many of the models give positive indications but not all – the library made use of a video platform that did not gain as high a usage as had been desired. At the end of the agreement period, the library was forced to use the upfront sum to purchase some video titles that had not had any usage at all, since usage had been too low to only purchase used titles. However, this can be compared with one e-book platform whose usage was so high that the library, at the end of the agreement period, purchased books that had been used more than twenty times during the period.

But even a successful EBS model should probably be deselected after a few years. The more years the library has had a model, the more e-books the library has purchased from the e-book platform at the end of each agreement period. This means that the library's percentage share of owned titles within the platform is constantly growing. At some point it should become unprofitable to continue with the model. For one of the PDA models, Stockholm University Library owned a full 22 per cent of the available titles, as measured in autumn 2015.

Would you like to find out more about the evaluation?

The report in full

The full text of the evaluation is found in the report “Evaluation of PDA and EBS models for e-books at Stockholm University Library” (reference number SU 525-2.19-0036-16). If you would like a copy of the report, please send us an e-mail.