LJ Index of Public Library Service Fact Sheet
Ray Lyons -- Library Journal, 2/15/2009
 |
For the latest data, see America's Star Libraries 2009, Round Two |
The LJ Index of Public Library Service is a new public library national rating system instituted by Library Journal and sponsored Baker & Taylor's Bibliostat Connect web-based statistical analysis software for public libraries. This 2009 edition of the LJ Index is based upon 2006 public library statistical data published by the Institute of Museum and Library Services.
The LJ Index rates U.S. public libraries with total expenditures of $10,000 or more that serve populations of at least 1000. Ratings are based on four per-capita service indicators:
- library visits
- circulation
- program attendance
- public Internet computer uses
Libraries must report all four statistical indicators to receive an LJ Index score. (For an FAQ, go here.)
LJ Index ratings divide libraries into nine peer comparison groups based on total operating expenditures. Within each group the highest scoring libraries are recognized using 5-star, 4-star, and 3-star designations. Each star-rating group contains ten libraries, except for the $30 million and above group for which each star-rating contains five libraries. Star ratings are based on Index scores.
Libraries are evaluated on each service indicator relative to the performance of other libraries in their peer group. The scoring compares each library’s four indicators to the peer group average for that indicator. The four indicators all receive equal weighting.
The LJ Index is offered as an overall indication of a library’s service performance relative to peer libraries. The statistical data LJ Index uses do not report the quality of services provided. Libraries should use LJ Index ratings in tandem with locally developed performance data.
All U.S. public libraries meeting the criteria outlined above have earned LJ Index scores. These scores and related information can be found on the LJ website.
The index is sponsored by Baker & Taylor’s Bibliostat, and dynamic access to the scores and associated data is provided exclusively by Bibliostat Connect.
Score calculation algorithm
LJ Index of Public Library Service scores are calculated as described in the steps below. Libraries must meet four inclusion criteria to receive an LJ Index score.
Step 1. For each library, per capita rates for the four statistical indicators described above are calculated. A per capita rate is defined as:
statistical indicator
--------------------------------------- = statistical indicator per capita rate
service area population
Example:
205,150 visits annually
--------------------------------------------- = 11.4 visits per capita
17,990 service area population
Step 2. For each of the of nine expenditure groups, mean (average) per capita rates for the four indicators are calculated.
Next, for each of the expenditure groups, the standard deviations of the four per capita indicators are calculated. A standard deviation is a statistical measurement of variation within a group of data—how spread out the data are.
Example results for the $200K-$399K peer (expenditure) group :
Mean visits per capita: 6.2
Standard deviation of visits per capita: 5.4
Step 3. A standard score (a statistical measurement known also as a “Z-score”) is calculated for each of a given library’s four per capita rates. Calculations take this form:
per capita statistic for given library – mean per capita rate for library’s peer group
---------------------------------------------------------------------------------------------------------------
standard deviation of per capita statistic for library’s peer group
Example for the $200K-$399K peer group:
11.4 visits per capita for this library
6.2 mean visits per capita for peer group
5.4 standard deviation of visits per capita for peer group
11.4 – 6.2
--------------------------- = .96 standard score for library’s visit per capita statistic
5.4
Note: Since the library’s visits per capita rate in this example is higher than the mean visits per capita for the peer group, the library’s standard score is positive. Had the library’s visits per capita rate been less than the peer group mean of 6.2, then the library’s standard score for visits per capita would be negative (less than zero).
Step 4. The four standard scores from step 3—one for each per capita rate—are summed.
Example for a given library:
.96 (standard score for visits per capita)
+ 1.57 (standard score for circulation per capita)
+ 1.10 (standard score for total program attendance per capita)
+ 1.51 (standard score for public Internet terminal uses per capita)
5.14 Library’s preliminary LJ Index score
Step 5. As noted in step 3, some libraries’ standard scores can be negative (less than zero), as can the preliminary LJ Index score. Among the entire 7,115 libraries rated, preliminary scores from step 4 included libraries scoring as low as -5.5. Therefore, a correction factor of 6 was added to all preliminary scores so that no LJ Index scores are negative.
Step 6. The final LJ Index score is calculated by multiplying the results from step 5 by 100 and then rounding to whole numbers.
Example for a given library:
5.14 + 6.0 = 11.14 (Preliminary score plus correction factor)
11.14 X 100 = 1114 (Final LJ Index score)
For more, go to the LJ Index main page.
