ABSTRACT
This chapter discusses the things to know, prepare, obtain, document, and assess before starting product design or evaluation. It serves as a checklist or a reminder with handy tips for the more experienced person and as a detailed guide for the novice. It is divided into three sections that match the inputs in the Sustainable Product Evaluation, Engineering, and Design (SPEED) process: (1) product, (2) resources, and (3) target population (TP). The product section discusses what we need to know about the product such as the product concept, how it is supposed to function, how it is expected to fit, and any constraints. The resources section discusses the tools needed, the personnel needed and their training, the facilities and test site considerations, as well as planning for data collection, data management, and maintenance. The TP section discusses how to represent and characterize the TP before, during, and after data collection.
Testing and gathering data on human subjects is a large part of the SPEED process enabling informed decisions throughout the process. Testing tells us what works and what does not, what is good and what is better, and what the users like and what they do not like. If we know these things early, it is less expensive to make changes than if we wait until the design is complete. If we wait until we are evaluating sizing for the finished product, it could be too late. Careful preparation allows us to avoid wasting time and money while doing this. Or as Benjamin Franklin once said, “A stitch in time saves nine”.
A large part of the preparation involves minimizing, controlling, and accounting for variability we do not want (error) such that with the help of probability theory and statistics, we can make good decisions. Whenever measurements are performed, no matter how carefully or scientifically it is performed or the quality of the measuring instrument, measurements are always susceptible to error and uncertainty. This is true even for measuring things that don't live, breathe, and change all the time. In the Metrology and Engineering fields, this is called Measurement uncertainty. Measurement uncertainty is an estimate of the level of accuracy and precision with which a measurement can be taken with a given tool or process.
Measurement uncertainty is one type of error. There are many sources of error including the tools used and their precision, the measurers and their training, environmental conditions, changes in the person being measured, measurement location, type of measurement, measurement method, clarity of measurement description, the sample size relative to the population size, and more. Unfortunately, these sources do not cancel each other out, but the error expands with each additional source. Therefore, it is important to do things to minimize or at least manage errors from each source. This begins with good preparation, which is a large part of this chapter.
