Sample plans comparisons for shelf life estimation using sensory evaluation scores

Sensory evaluations to determine the shelf life of food products are routinely conducted in food experimentation as a part of each product development program, whether it includes a new product, product improvement or a change in type or specification of an ingredient. In such experiments, trained panelists are asked to judge food attributes by reference to a scale of numbers. The “failure time” associated with a product unit under test is usually defined as the time required to reach a cut‐off point previously defined by the food company. Important issues associated with the planning and execution of this kind of testing are total sampling size, frequency of sample withdrawals, panel design, and statistical analysis of the panel data, to list a few. Different approaches have been proposed for the analysis of this kind of data. In particular, Freitas et al. proposed an alternative model based on a dichotomization of the score data and a Weibull as the underlying distribution for the time to failure. Also, through a simulation study, the bias and mean square error of the estimates obtained for percentiles and fraction defectives were evaluated. These quantities were used to estimate the shelf life. The simulation study used only the same sample plan implemented in the real situation. This paper focuses on the planning issues associated with these experiments. Sample plans are contrasted and compared in a simulation study, through the use of the approach proposed by Freitas et al.. The simulation results showed that, in general, one can get results much more precise and with smaller bias with a shorter follow‐up time, allocating more panelists to each evaluation time.