Thursday, August 9, 2007

PL 27/07: Ups and downs in lending

Filed under: statistics — plinius @ 12:20 pm

bibliofil.gifMost libraries expect systematic variations in demand through the day, through the week and through the year.

For Norwegian public libraries we get a clear indication of the annual cycle from a diagram published by Bibliofil (right).

Bibliofil is the most widely used data system in the public library sector, with a market share (percentage of all loans) around 65 %. The diagram shows aggregated loans for the 52 libraries that have used Bibliofil since 1996. These 52 units counted for two thirds of all Bibliofil loans in 2006.

I have analysed the monthly statistics in the period 1996-2005 – and can report the following:

The average number of loans was 895 thousand per month. But the monthly traffic varied from an average of 656 thousand in July to 1.060 thousand in October.

The relative levels were as follows:

  1. January: ………..116 %
  2. February: ………107 % – corrected 117%
  3. March: …………..114 %
  4. April: ………..…..101 %
  5. May: ………….…..89 %
  6. June: ………….….84 %
  7. July: ………………73 %
  8. August: …………..91 %
  9. September: …….109 %
  10. October: …………118 %
  11. November: ……..115 %
  12. December: ………..81 %

July is the cruellest month, could T.S. Eliot have said – followed by December.

Added March 4, 2012

In Norway, libraries without electronic counters are asked to estimate the annual number of visits from manual counts in weeks 14 and 39. These weeks fall in late March and late September, respectively.  If the number of visits is proportional to the number of loans, the annaul estimates will be too high by twelve percent or more.  


The overall pattern is clear. The data could be refined by:

  • correcting for the different length of each month
  • correcting for Easter and other moveable feasts
  • correcting for the varying number of Sundays in each month

If we take the average month as 30,5 days, the corrected level for February would be 117 %. Easter oscillates between March and April – but not on a 50/50 basis! The full table shows that Easter lowers the lending of the month in question by about ten percent. Norwegians take their Easter vacations very seriously!

With these corrections we can describe the lending pattern as follows:

  • high lending levels – above 115 % of the annual average – in January-March and in October-November
  • low levels – below 85 % of the average – in June, July and December
  • medium levels in April, May, August and September



1 Comment »

  1. […] 27/07. Ups and downs in lending. Monthly loans from Norwegian public […]

    Pingback by P 8/12: News from the North « Plinius — Sunday, March 4, 2012 @ 10:33 am

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