thermal fluctuations cause proteins to adopt an ensemble of conformations wherein the relative stability of the different ensemble members is determined by the topography of the underlying energy landscape . 
 folded  proteins have relatively homogeneous ensembles , while  unfolded 
 proteins have heterogeneous ensembles . 
 hence , the labels  folded  and  unfolded  represent attempts to provide a qualitative characterization of the extent of structural heterogeneity within the underlying ensemble . in this work 
 , we introduce an information - theoretic order parameter to quantify this conformational heterogeneity . 
 we demonstrate that this order parameter can be estimated in a straightforward manner from an ensemble and is applicable to both unfolded and folded proteins . 
 in addition , a simple formula for approximating the order parameter directly from crystallographic b factors is presented . by applying these metrics to a large sample of proteins , 
 we show that proteins span the full range of the order  disorder axis .