Methods and respective modules which reduce sample size and measurement duration of metrology parameters by selecting a relatively small subset of measured targets to represent a distribution of parameter measurements of a large number of targets. The subset is selected by sampling a substantially equal number of measurements from each of a selected number of quantiles of the distribution. The methods and modules allow identification of targets which represent correctly the whole target measurement distribution. The methods and modules optimize quantiles and sample size selections, using accuracy scores and estimations of the robustness of the selections. Sampling and selections may be carried out iteratively to reach specified criteria that match the results which can be derived when considering the whole distribution.