Counting every day is therefore impossible (except for very small libraries). Instead, libraries must select a small number of counting days, during which everybody is counted. These data are used to calculate the average number of visits per day.
If the library keeps open 250 days per year (say), we multiply the average by 250 to get the annual total.
Small and medium
In small libraries it may be possible for the librarian on duty to do the counting in addition to her or his regular work. But it takes an extra effort. Medium-sized libraries must probably assign a staff person (on rotation) to sit near the entrance throughout the day.
Weeks or days
Library authorities often recommend to do one full week of counting in the spring and one in the autumn. From a statistical point of view it is better to disperse the counting days, however. The library could for instance select one day in January, one day in February, and so on.
Dispersed days provide more accurate data, since they are less influenced by external events and seasonal fluctuations.
The cost of data collection
If the library keeps open (say) five days a week, this means – in any case – devoting ten full work days to data collection.
If the observer only counts the number of vistors, the library spends ten days of work to calculate a single figure – the annual number of visitors. That is not a very productive process. The cost is high and the benefit low.
Some libraries reduce the work load by counting for two days rather than two weeks. But this approach makes the figures very uncertain. Your annual visitor numbers will go up and down for no particular reason. Two single days cannot “represent” a full year in a faithful way.
It is better, I believe, to spend two full weeks, but to use those weeks to get broader and deeper data that can be used for advocacy and planning. The cost remains high – but we improve productivity by increasing the statistical benefit.
Counting and observing
Manual counting is based on direct observation.
Electronic counters can only tell you how many people visit the library. If you want to know who these people are, what they do and how long they stay, you need to observe them.
Such data are very useful for advocacy. It is also easy to combine them with stories about individuals and their benefits from using the library.
Manual counting is more than an alternative to electronic counting. It is the first step towards systematic observation.
Count The Traffic
I hope to write more on simple observation methods in libraries during the summer. In the meantime I refer to the English language home page for the the project Count The Traffic (CTT), with related pages and publications.