[library-media] VERY INTERESTING FOLLOW UP - School Library Impact Bragging Rights

Juan Lee jtlee at utah.gov
Wed Feb 15 13:25:03 MST 2012

Please excuse the follow up and cross-posting. -- Juan Tomás Lee

If you haven't seen them yet, don't miss Linda Hofschire's and my two
latest publications about school librarians and their impact on national
and state test scores.  See

To address Bruce's question, we generally see similar results for
reading and writing scores.  Occasionally, the two are combined in
'language arts' scores.  I don't know that anybody has looked at math
scores.  As for why the host of other state test scores tend not to be
examined (e.g., history, geography, science), the usual reason is that
test scores for subjects other than reading (and in some states, writing
and math) are not nearly as widely available as reading scores.

As for the correlation vs causation issue, it's true; correlation is
not causation.  But, most of the extant studies about school library
impact -- see http://www.LRS.org/impact.php -- are not simple
correlational studies.  They usually take into account other control
(ie, 'competing cause') variables, including
-- other school conditions, such as per pupil spending and
teacher-pupil ratio, and
-- community conditions, such as poverty, adult educational attainment,
and racial/ethnic demographics.

The trend across two dozen plus studies has been that the two most
consistent predictors of test scores are 1) poverty and 2) school
libraries.  Poverty tends to 'soak up' the impact of the other control
variables, most of which are highly correlated with how rich or poor a
school is.  My theory about why school libraries exert a measurable
independent impact is site-based management.  If you know how rich or
poor a school is, you can make a good guess at most of the control
variables.  Knowing a school's funding rarely assures one of anything
about the quality of its school library program.  It's usually a matter
of whether or not there's a top-notch librarian and whether or not
teachers and administrators 'get it.'  (As I always say to administrator
audiences:  You think you know why I'm here--to ask you for dollars and
FTEs.  It is SO much worse than you think … I want your HEARTS and

So, if anyone's response to you about the school library impact studies
is that they are 'merely correlational,' please correct this
misconception, as it's just not true.  While they are not (and couldn't
have been) experimental studies, and while no single study can claim to
have proven causality, we believe that the reliability of the findings
across many states, using control variables, makes a compelling argument
for causation.

Notably, in Linda's and my SLJ article -- looking at the relationship
between pre-/post-Recession changes in librarian staffing and changes
over the same interval in National Assessment of Educational Progress
reading scores -- a new 'control' variable is considered:  total school
staff change.  Given a correlation between change in scores and change
in librarian staffing, a skeptic could argue that change in librarian
staffing might just be a proxy for total school staff change. 
Interestingly, when we controlled for total staff change, the strength
of the link between librarian change and score change was not weakened
significantly.  (Indeed, while we didn't report it directly in that
article, there was NO significant correlation between total school staff
change and reading score change!)

I hope this information is useful.  If it still leaves you with
questions, please contact Linda or me.

PS--As you'll see on the linked page, the RSL Research Group is
conducting a new study in PA this year.  I'll try to remember to keep
you posted about it on this list.  Otherwise, watch my website for

Keith Curry Lance
RSL Research Group
mobile 720-232-5866
keithlance at comcast.net 

On Feb 15, 2012, at 12:24 PM, Pomerantz, Bruce (MDE) wrote:

Okay, I know that that correlation is not causation.  However, take a
look at the graphs which a department statistician created based on 2011
standardized reading test scores. The density plot graph is the best
eye-grabber. I wonder if a similar impact would show up with the math
scores.  Hmmmm.

Bruce Pomerantz, Library Development Specialist
State Library Services - D29
Minnesota Department of Education
1500 Highway 36 W.
Roseville, MN 55113
Phone: 651-582-8890
Email: bruce.pomerantz at state.mn.us 
Fax: 651-582-8752

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