Executive  summaryChapter1Chapter2Chapter3


Usage Patterns

Charts 1-4 present the circulation totals by week for each slide library. For week numbers and their corresponding date see Appendix 5CBreakdown of Week Numbers by Date.

Chart 1: Slide Library 1

Chart 2: Slide Library 3

Chart 3: Slide Library 4

Chart 4: Slide Library 5

The charts illustrate that there are roughly two peaks of high usage each semester. The exact points at which these start and finish vary slightly from institution to institution. This variance can be explained in part by the fact that at Slide Library 4, the statistics were the number of slides checked out while at the other libraries, it was the number of slides re-filed. Also, Slide Library 1 is on a quarter system, so it has very different peaks and valleys.

Table 1: Academic calendar for each slide library

Interestingly, at Slide Library 1, which is on a quarter system, the peaks in usage occur at the same time during both quarters; during the 4th and then again during the 9th week of classes. In the winter quarter, the first peak is during week 5, then again during week 10. During the spring quarter, the peaks appear during week 17 and week 22.

Slide Libraries 3 and 5 demonstrate an increase in use during weeks 8 and 7 respectively, but the first peak of usage for both is during week 10. At Slide Library 3, the second peak in usage is during Week 16, while at Slide Library 5 there are two peak times; one during week 15, then again during week 18.

Since the statistics provided by Slide Libraries 1, 3, and 5 are those of slides returned, it is not surprising that there are many slides returned after the semester/quarter is over. For example, at Slide Library 1, during week 12, which is final exam week, 3,851 slides are re-filed-the highest number. One could speculate that during and after final exams, faculty members are returning slides used during the term.

In contrast, at Slide Library 4, where the statistics accounted for slides checked out, there is an immediate decline in slide circulation after the semester is over. At this slide library, there is only one peak of usage during the first half of the semester, during week 7; whereas during the second half of the semester there are two peak times, during weeks 16 and 17.

Usage Totals

Table 2 presents the usage totals taken from Charts 1-4. It is beyond the scope of this article to fully examine each library to explain in detail why there is a divergence in total numbers. In brief, the reason for the difference in total numbers between Slide Library 1 and the other libraries is that their numbers reflect both slides that actually leave the library and slides that have been browsed through. At Slide Library 4, statistics are for images that have been checked out, and do not include the number browsed through. In fact Library 4 estimates that approximately 2,500 slides are re-filed a week, so that would put them at a number similar to Slide Library 1around 50,000 slides a semester. A final note is that at Slide Library 3, due to their check out policy (see Appendix 5A-Slide Library Profiles) there are slides in circulation that are not reflected in these numbers.

The issue of the number of slides checked out as opposed to the number of slides that are browsed is an important one. Unfortunately we don't have exact figures for these statistics, with the exception of Slide Library 4 which has approximately 13,600 slides per term checked out, and approximately 2,500/week re-filed, roughly a 4:1 ratio. This ratio reflects the fact that users of slide libraries tend to browse through the slides in order to find the needed slide rather than consulting a catalog.

Table 2: Usage totals

In the following two sections, we look at the users by class of user (primary, secondary or other), then examine their usage patterns by month. These statistics were only available from Slide Libraries 1, 4, and 5.

Percentage of Users

Table 3 presents the percentage of usage by primary, secondary and other users. These percentages represent the number of slides used by the various groups, not the number of users in each group.

Primary users in each library represent the core departments served, while secondary users are related departments. For example, at Slide Library 1, Architecture and Art History departments represent their primary users while Fine & Applied Arts users were classified as secondary users. It is interesting to note the "other" users represent a significant percentage of usage for each slide library. This indicates that, to some extent, they all serve departments that are not strictly within the scope of their parent departments. At Slide Library 1 "other" usage is 8% of usage (some of the "non-regular users" could be considered other users so this percentage might in fact be higher).

Table 3: User breakdown

1 At slide library 1, the "non-regular" users come from a variety of departments. They represent users who do not use the library on a regular basis so they are not assigned a check-out card. These users can be from the core departments like Art History or from other departments. For example, they can be undergraduates taking an Art History course, or they can be faculty from another department that is using the library only occasionally.

2 The new slides and rebinds are the percentage of new slides that are re-filed each month and the number of slides that have been rebound that are re-filed.


Percentage of Usage by Month

Tables 4, 5, and 6 show the percentage of usage by month by class of users. Since we only gathered data for one semester it is difficult to come to conclusions about the usage patterns. However we do see that there is a different pattern of usage between the primary and secondary and other users. The primary users represent constant usage throughout the term. In contrast, there are no clear usage patterns by secondary and other users across the various slide libraries.

Table 4: Slide Library 1: Percentage by month of usage

3 See footnote 1

4 See footnote 2


Table 5: Slide Library 4: Percentage by month of usage

Table 6: Slide Library 5: Percentage by month of usage

Back to Chapter 5


The Cost of Digital Image Distribution:
The Social and Economic Implications of
the Production, Distribution, and Usage of Image Data

By Howard Besser & Robert Yamashita