Hoarding is not collection development
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Making a Collection Count

Practical Librarian

This is the place that we put more serious discussions of librarianship.

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Collection Analysis: Median vs. Average

There is more to understanding a collection age beyond average and thanks to Emma, who made a comment on my last collection analysis post, I thought it would also help to discuss median age in a collection. My experience has been that often “average” and “median” are used interchangeably (which is so very wrong!).  Median age of a collection really has some serious power in helping librarians talk about collection age.

First, let us get clear on the difference is between median age and average age of a collection. (Again, as I have done in previous posts, the best way to get a handle on the process is to use a small set of numbers until you feel comfortable.) The average is the sum of all the dates in the set divided by the number of items in the set. (If you are using Excel, it will be the @average function)

Here is the example of some publication dates:

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Collection Metrics Part 2: Dewey Call Numbers

spine labelsNow that we’ve talked about using publication dates, let’s talk about metrics that use call numbers. What do we still have in the collection after that big weed? It’s too big a chart to include here, but I can tell you that the top three subject area holdings in my 500s are:

1. 599 Mammals – 161 items
2. 551 “Geology, hydrology, meteorology” – 153 items
3. 523 “Specific celestial bodies and phenomena” – 139 items.

Now we need to find out where the holes in the collection are. Still sorted by call number, we look at the subject areas that have very few holdings and decide if they are popular enough to warrant buying more items in those areas. There isn’t necessarily a lot of quantitative data to help you make this decision. I feel like I’m aware enough of my community’s needs (curriculum, local clubs, common reference questions, collection policy) to make an educated guess about what subject areas we need more materials in and which ones we don’t. We also have collection management guidelines and a selection policy to follow.

The bottom three subject area holdings in the 500s are:
1. 562 Fossil invertebrates – 1 item
2. 565 Other fossil invertebrates – 1 item
3. 596 Vertebrata – 1 item

We have plenty of items on vertebrate fossils, but apparently very little on invertebrate fossils. Ok, we’ll try to buy a few.

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Collection Metrics: Using Publication Date

old booksI maintain the adult non-fiction 500s in my library. I normally let an Intern have their way with my collection, so it gets a concentrated weed at least annually. I also believe that collection management should be on-going, so I am constantly picking at the 500s. In that regard, there’s rarely something truly awful in the 500s. There are some lingering items that haven’t circulated well, or that are on schedule to be weeded the following year, but I deal with items in bad condition and unnecessary duplicates on an ongoing basis.Here’s how it works for the annual Intern weeding project:

1. What hasn’t circulated in three years? Weed ’em. I am fortunate to have a budget, space, and patron demand that can keep up with a three-year cycle. Of course, the Intern and I still look closely at what is showing up in this report. We don’t just weed everything that hasn’t circulated in three years. Some things are left alone for another year or two, depending on what they are and their purpose.

2. What is older than ten years? Depending on the subject area and its dependency on currency, weed ’em. For example, many math books, plant books, and animal books are ok up to (and even beyond) ten years. There are also some classics (for example, Stephen Hawking’s older books) that are going to be kept for a while yet too.

3. What is older than five years? See #2. These are more timely categories. Pluto kicked out of the planet club? Weed ’em.

Now it’s time for some metrics! We’ve removed the dead weight based on the above criteria, and a new shelf list is run for the 500s. Using Excel, it is sorted by publication date (or “date created” if you’re using the ILS I’m using, since that’s all we have to work with. Seriously.)

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