Methods relating to profiling and/or identifying molecules in a sample, particularly chemical or biological molecules contained in an experimental sample using measured data about molecules actually present and known information about candidate molecules that may be present. Information tags can be assigned to candidates. This may be achieved with a high degree of accuracy and a low false positive rate by minimising the effect of one or more possible sources of error. An objective goal (assignment) may be optimised by linear programming or by mixed integer programmin