Perhaps the most important finding of Figure is the field-reported data of Lukawski et al. (2014) and the bottom-up models (GETEM/GeoVision) tend to agree within 20% on well cost. The greatest difference is the field-reported Klein et al. (2004) data; however, this dataset had low correlation ( 0.558) and thus presumably it was corrected and included in Lukawski et al. (2014), where it had a higher correlation ( 0.92).