Friday 30 December 2016

The school research lead and the half-life of facts - why everything we know has an expiration date

One of the main reasons why school leaders need to be constantly engaged in evidence-based practice, is that the evidence we might use to support decisions can become ‘rusty’ (Hargreaves and Fullan, 2012).   Evidence that we have relied on in the past may no longer be current or applicable, indeed advice based on the evidence may have just been plain wrong.  Indeed, (Arbesman, 2012) argues that just like radioactive material, ‘facts’ have a half-life and decay over time.  Arbesman states:

Facts, in the aggregate, have half-lives: We can measure the amount of times for half of a subject’s knowledge to be overturned.  There is science that explores the rates at which new facts are created, new technologies are develop, and even how facts spread. (p3)

To illustrate this point, Arbesman cites the work of (Poynard et al., 2002) who demonstrate that in a particular field of medicine – cirrhosis and hepatitis -  that the half-life of facts in this field was approximately forty-five years.  In other words, half of what we thought we knew about cirrhosis and hepatitis was within forty-five years been shown to be incorrect. 

Now in the context of social science – within which much educational research finds a home – the half-life of facts is generally shorter than forty-five years.  – in part because of some difficulties associated with undertaking social science and trying to distinguish the signal from the noise (Silver, 2012).  In other words, the conduct of social science is much messier than the physical sciences, making it much more difficult in establishing ‘incontrovertible facts’.

So what is the importance of being aware of the half-life of facts.  Arbesman argues that being aware of how facts change, develop and spread is important in that facts – however defined, help us make sense of the world we are facing.  If we are aware of how facts change and develop over time, it will allow us to be more critical of the evidence on which we base decisions, as it will help us identify the both limitations of that evidence and what actions we can take to offset such limitations.   

However, in the context of being an evidence-based school leader, being aware of the half-life of facts has a number of important implications.  First, the need for for school leaders to be constantly searching for the best available evidence, recognising what is the best available evidence is constantly changing.  Second, evidence-based school leaders may have to act on the basis of that much of what research evidence suggests works, may in the long-run turn out to incorrect.   Indeed, there may-be parallels between educational research and the old saying about advertising expenditure, fifty percent works, fifty percent doesn’t, trouble is we don’t know which is which. Consequently, evidence-based school leaders need to proceed with a large-degree of humility.  Third, evidence-based school leaders are going to need to be able to adapt to a world of changing facts, and what was certain at the beginning of their working life, may be less so towards the end of your career.   What was once ‘cutting-edge’ may now be just a jagged old ‘rusty-edge.’   Finally, and probably most importantly, evidence-based school leaders will need to contribute to developing an evidence-based school culture, where all staff are constantly challenging what they think, and in doing so provide conditions for effective and stimulating professional learning for teachers, at all stages  of their career.


ARBESMAN, S. 2012. The half-life of facts: Why everything we know has an expiration date, Penguin.
HARGREAVES, A. & FULLAN, M. 2012. Professional capital: Transforming teaching in every school, Teachers College Press.
POYNARD, T., MUNTEANU, M., RATZIU, V., BENHAMOU, Y., DI MARTINO, V., TAIEB, J. & OPOLON, P. 2002. Truth survival in clinical research: an evidence-based requiem? Annals of internal medicine, 136, 888-895.

SILVER, N. 2012. The signal and the noise: the art and science of prediction, Penguin UK.


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