**Figure 1**
Schematic representation of conditional probability distributions of structure factors. (*a*) Probability distribution (represented by grey shading) of structure factor **F**_{1} given a related structure factor **F**_{2}. The distribution, given in (1), is centred on *D***F**_{2}, where *D* represents the fraction of **F**_{2} that is correlated with **F**_{1}. The width of the distribution is described by the parameter σ_{Δ}. (*b*) Probability distribution (represented by grey shading) of **F**_{j} (structure factor for derivative *j*) given an assumed true native structure factor **F** and the structure-factor contribution **H**_{j} computed from a heavy-atom model. The distribution, given in (5), is centered on *D*_{j}**F** + **H**_{j}. The width of the distribution includes contributions from lack of isomorphism, errors in the heavy-atom model and measurement error. |