A THIRD NOTE ON AGEING IN A LIBRARY CIRCULATION MODEL: APPLICATIONS TO FUTURE USE AND RELEGATION
| Date | 01 January 1987 |
| DOI | https://doi.org/10.1108/eb026799 |
| Published date | 01 January 1987 |
| Pages | 24-45 |
| Author | QUENTIN L. BURRELL |
| Subject Matter | Information & knowledge management,Library & information science |
A THIRD NOTE ON AGEING IN A LIBRARY CIRCULATION
MODEL: APPLICATIONS TO FUTURE USE AND RELEGATION
QUENTIN L. BURRELL
Statistical Laboratory
Department
of
Mathematics,
The
University,
Manchester,
M13 9PL
The Burrell and Cane mixed Poisson model for library loans is used to predict
future use of items in a collection. The model is also used to investigate possible
relegation procedures based on frequency-of-circulation data.
1.
INTRODUCTION
IN AN EARLY PRESENTATION of the mixed Poisson model for library
loans,
Burrell1 argued that previous use of items in a library collection, as
measured by recorded frequency-of-circulation (FOC), could be used as a predic-
tor of future use and hence could be adopted
as
a guide to relegation decisions. In
particular it was shown how this approach could lead to quantitative assessments
being made of the likely degree of
recall
of relegated stock
as
well as the resulting
change in FOC of retained stock.
Two major drawbacks of this simple formulation are:
(i) only a geometric form for the FOC distribution of
usage
within a given
period was considered,
(ii) it was assumed that items do not age, in the sense of their becoming less
frequently borrowed on average as time goes on.
So far as (i) is concerned, this limitation was recognised by Burrell2 and Burrell
and
Cane3
and, particularly in the context of the proposed relegation procedure,
the crucial role of
this
assumption was highlighted by Hindle and Worthington.4
The more general formulation of Burrell and Cane which leads to a negative
binomial distribution (NBD) for the FOC distribution (see also Bagust5 and
Ravichandra Rao6) was further investigated by Burrell7,8 specifically to incor-
porate the empirical phenomenon of ageing of library materials.
In this paper the mixed Poisson model incorporating ageing as previously
presented7,8 is applied to issues of prediction and relegation
as
considered by Bur-
rell.1
Technical details are given in the Appendix.
2.
PREDICTION AND RELEGATION
Anyone writing on the vexed issue of removal of stock from open access shelving
to
a
more restricted location does so in the knowledge that, whatever suggestions
are made, they are unlikely to be welcome. We may talk of relegation, retirement
or weeding of the stock or, a more recent description, the de-acquisition of items
but, no matter how gentle the euphemism, 'the idea', to quote Turner,9 'of
Journal
of
Documentation,
Vol. 43, No. 1, March 1987, pp. 24-45.
24
March
1987
CIRCULATION MODEL
removing
a
conscientiously acquired volume wreaks havoc with the innards'. It is
not our purpose to argue the rights and wrongs of relegation but rather to in-
vestigate a procedure which, if relegation is to be implemented, can lead to quan-
titative assessment of possible effects.
It seems that most approaches to relegation are in essence either subjective or
scientific, or some combination of the two. The subjective approach requires that
each individual candidate for relegation must be proposed by, and the actual deci-
sion taken by, an expert or experts. This undoubtedly
is
the traditional viewpoint
of the librarian in that it surely defines one of the roles of the librarian as the
'keeper of the collection'. Scientific approaches require information about certain
characteristics of past and current performance of the collection and then seek to
identify particular items which, using one criterion or another, are not achieving
an acceptable level of performance. We shall not attempt to survey all previous
work in the field; such surveys may be found in Seymour10 and Slote.11 Nor shall
we concentrate in detail on the subjective approach. An example of this, with
some concession to the scientific approach also, may be found in the monograph
by Ash.12
While acknowledging the role of the expert, Fussier and Simon13 seem to be
the first wholehearted supporters of the scientific approach, a preliminary version
of their work being circulated in
1961.
The basic tenet of the scientific approach is
that one should identify those items whose expected future use is likely to be so
low that the problem reduces to one of predicting future use, which in turn re-
quires that appropriate predictors be found. Fussier and Simon found that
previous use was the best single predictor of future use and this is the standpoint
we shall adopt. Other authors such as Jain
et
al.14 and
Morse15
have felt that age of
items is of importance but we shall not explicitly include this in our considera-
tions.
Perhaps the most widely published method based on past use is one developed
and described in a series of papers by Trueswell16-18 and subsequently by
Turner.19,20 Trueswell's method relies on data relating to the time at which an
item was last circulated and has been the subject of some practical studies. (Some
of
the
pitfalls for both the proponent and the practitioner of the scientific method
can be seen in the recent exchanges involving Sargent,21 Trueswell,22 and
Turner.9)
In our model, to be discussed in subsequent sections, the required data on
previous use involve the number of circulations of
items,
and on the basis of these
we make our predictions regarding future use. Note that, as may have been im-
plicit in the foregoing, we are restricting our attention to monographs and their
use in large academic research libraries. We do not address the problem of relega-
tion of journals (for
a
survey of work in this area we refer the reader to Seymour23)
nor do we consider the problems of public lending libraries whose purpose, and
mode of operation, are rather different.
3.
LONGITUDINAL STUDIES
3.1
Preliminaries
In this study we are concerned with the use made of monograph collections,
where use is determined by circulations/transactions, meaning external borrow-
ings as opposed to consultations or other uses made within the library. By items
we mean individual volumes rather than titles so that, for instance, multiple
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