Economics and Usage of Digital Libraries: Byting the Bullet

26. The calculations in the two columns are independent and should not generally sum to one. The first column indicates the percent of titles that were subscribed that should have been subscribed (given perfect foresight). A high percent means there were not many specific titles subscribed that should not have been. However, this does not indicate that a library subscribed to most of the titles that it should have. A library that subscribes to zero journals will get 100% on this measure: no journals were subscribed that should not have been. The second column addresses this question: what percent of those titles that should have been subscribed were missed? The two columns correspond to Type I and Type II error in classical statistical theory. The first should be high, and the second low if the institution is forecasting well (and following our simple model of "optimal" practice).