The present invention provides a plurality of samples, each of which includes particles of a predetermined particle dimension, within narrow predetermined limits, dispersed in a carrier at a predetermined particle concentration. The predetermined particle dimension and the predetermined particle concentration are the same for each sample. However, advantageously, each sample has a different predetermined ratio of a value of an optical property of the particles to a value of the same optical property of the carrier. The present invention also provides a method for selecting a target sample from the plurality of samples to assess the measurement accuracy or the detection sensitivity of an optical particle analyzer as the predetermined ratio approaches 1.