• http://www.findarticles.com/cf_0/m0961/v49/21036269/print.jhtml
  Bias in the Interpretation and Use of Research Results.
  

• http://trochim.human.cornell.edu/kb/external.htm
  William Trochim's page on external validity.
  

• http://www-class.unl.edu/psycrs/new350/unit1/extval/sld001.htm
  Here is a nice PowerPoint presentation on external validity.
  

• http://www.apa.org/journals/com.html
  The Journal of Comparative Psychology.
  

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