11. Formally, Normalized Paid Access is equal to , where Apaid is the total number of paid accesses, Aunmetered the total number of unmetered accesses, and Scale is equal total number of free accesses divided by the total number of accesses of free content in journals to which the institution does not have a traditional subscription. We multiply by Scale because the more that accesses are covered by traditional subscriptions, the less likely a user is to require paid access. Scaling by access to unmetered content also controls for different overall usage intensity (due to different numbers of active users, differences in the composition of users, differences in research orientation, differences in user education about PEAK, etc.). Unmetered accesses proxies for the number of user sessions, and therefore our statistic is an estimate of paid accesses per session.
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