Good discussion to give reason for less accuracy in terms of less no. of samples but greater variation

"Page 93: However, the results were not as good as previously reported, when samples were all taken from one field including three textures only. This was considered due to the smaller number of samples used, involving greater variation of soil texture and colours."

(Mouzzen et al., 2005. Near infrared spectroscopy for agricultural materials: an instrument comparison, J. Near Infrared Spectrosc. 13, 87-97.)