Thorndike, E. L. (1904). Sources of error in measurements. In E. L. Thorndike, Library of psychology and scientific methods. Theory of mental and social measurements (pp. 157-162). : The Science Press.
http://dx.doi.org/10.1037/13283-011
So far our supposition has been that the measures with which we start are accurate representatives of the fact measured, that A really did misspell the word which we score misspelled, that B did really take the .150 sec. to react which the chronoscope recorded, that the school enrollment and average attendance given for cities in the U. S. Commissioner's report give the real facts, that the number of children recorded in certain genealogy books for certain families were the real numbers. Our problem has been to make the best use of the data and introduce no error in manipulating them. But that a measure should thus perfectly represent a fact, the fact must be measured by a perfect instrument used by an infallible observer. In reality, any measure is a compound of a fact and the errors which the .instrument and observer will surely make. (PsycINFO Database Record (c) 2016 APA, all rights reserved)