 When combined with kinetic data on folding, the "m"-value can be used to roughly estimate the amount of buried hydrophobic surface in the folding transition state.Unfortunately, the probabilities formula_13 and formula_14 cannot be measured directly.Instead, we assay the relative population of folded molecules using various structural probes, e.g., absorbance at 287 nm (which reports on the solvent exposure of tryptophan and tyrosine), far-ultraviolet circular dichroism (180-250 nm, which reports on the secondary structure of the protein backbone), dual polarisation interferometry (which reports the molecular size and fold density) and near-ultraviolet fluorescence (which reports on changes in the environment of tryptophan and tyrosine).