Usually people do not ask for adequateness but whether the fit is "good" or, worse, "bad". But "good" or "bad" are not properties of the fit or the data. The data allow for a certain residual value (R value) depending on the amount of noise contained in the data. The simplest way to answer the question is therefore to calculate a theoretical R value that gives the R value approximately attainable with the given dataset including the standard uncertainties. When the R value from the least squares fit is much smaller than this theoretical R value, overfitting has occurred. When the R value from the least squares refinement is much larger than the theoretical R value, systematic errors apply. More about this topic is found in the November 2013 issue of Acta Crystallographica Section A (Volume 69, Part 6), doi:10.1107/S0108767313022514.