1 Using the variance structure of the conditional autoregressive spatial specification to model knowledge spillovers
Olivier Parent , James P. LeSage
Journal of Applied Econometrics
Volume 23, Issue 2, pages 235–256, March 2008
http://onlinelibrary.wiley.com/doi/10.1002/jae.981/full

2 QUANTIFYING KNOWLEDGE SPILLOVERS USING SPATIAL ECONOMETRIC MODELS
Corinne Autant-Bernard , James P. LeSage  
Journal of Regional Science
Volume 51, Issue 3, pages 471–496, August 2011
http://onlinelibrary.wiley.com/doi/10.1111/j.1467-9787.2010.00705.x/full

3 Regional knowledge spillovers: Fact or artifact?
Gottfried Tappeiner , Christoph Hauser ,  and Janette Walde
Research Policy
Volume 37, Issue 5, June 2008, Pages 861-874
http://www.sciencedirect.com/science/article/pii/S0048733308000358