[en] Factorial design and Fractional Factorial design methods are described and example test matrices are presented. The application of the fractional factorial design to a particular series of experiments planned to study mixing of melt and water is described. The advantages and disadvantages of using a fractional factorial scheme compared to using a one-factor-at-a-time scheme are discussed. Methods of determining which factors and interactions have an effect on the outcome of the experiment are described. The methods described here can be applied to any situation where information about the effect of several factors, on a single test statistic is required in as few as possible experiments. (author)