A method of screening for a binding interaction comprising the steps of: preparing multiple sets of uniquely identifiable microparticles wherein the microparticles within a set have the same unique identifiable characteristic and further, wherein one or more sets comprise two or more subsets of microparticles, each of said subsets presenting at least one unique probe that acts as a binding partner for a target molecule within a biological sample, wherein the number of probes varies between the subsets and at least two of the subsets of microparticles within at least one of the sets of uniquely identifiable microparticles are present in a fixed numerical ratio other than about 1 to 1; contacting said multiple sets of microparticles with a biological sample under conditions in which a target molecule within the biological sample binds to the probe, detecting the binding of a target molecule within the biological sample and the probe on said microparticles by generation of a signal indicative of the binding interaction between the target molecule and the probe, measuring the signal indicative of the binding interaction for said microparticles, selecting a proportion of less than 100% of microparticles exhibiting the greatest signal indicative of the binding interaction for one or more sets of uniquely identifiable microparticles, determining for said set(s) of uniquely identifiable microparticles whether the signal indicative of the binding interaction for the selected proportion is greater than a selected threshold indicative of the presence of one or more target molecules in said biological sample; and determining the number of uniquely identifiable microparticle sets indicating the binding interaction. preparing multiple sets of uniquely identifiable microparticles wherein the microparticles within a set have the same unique identifiable characteristic and further, wherein one or more sets comprise two or more subsets of microparticles, each of said subsets presenting at least one unique probe that acts as a binding partner for a target molecule within a biological sample, wherein the number of probes varies between the subsets and at least two of the subsets of microparticles within at least one of the sets of uniquely identifiable microparticles are present in a fixed numerical ratio other than about 1 to 1; contacting said multiple sets of microparticles with a biological sample under conditions in which a target molecule within the biological sample binds to the probe, detecting the binding of a target molecule within the biological sample and the probe on said microparticles by generation of a signal indicative of the binding interaction between the target molecule and the probe, measuring the signal indicative of the binding interaction for said microparticles, selecting a proportion of less than 100% of microparticles exhibiting the greatest signal indicative of the binding interaction for one or more sets of uniquely identifiable microparticles, determining for said set(s) of uniquely identifiable microparticles whether the signal indicative of the binding interaction for the selected proportion is greater than a selected threshold indicative of the presence of one or more target molecules in said biological sample; and determining the number of uniquely identifiable microparticle sets indicating the binding interaction.