Earlier in this book, and particularly in Chapter 12, I mentioned testing and by association conducting experiments. This implies that data are being collected and analyzed in order to make engineering or business decisions. The focus of this chapter is to take a closer look at data, data collection, and to provide guidelines on how to examine the impact of inputs on output; otherwise known as cause and effect; to ensure that all elements impacting the outcome of the test results are considered and accounted for so that, paraphrasing Edward Tufte (1997), it is an experiment and not merely an experience!