Statistics is the science and art of making decisions based on quantitative evidence. This introductory chapter motivates the study of statistics by describing where and how it is used in all endeavors. It gives examples of applications, a little history of the subject, and a brief overview of the structure and content of the remaining module.
Almost all fields of study (including but not limited to physical science, social science, business, and economics) collect and interpret numerical data. Statistical techniques are the standard ways of summarizing and presenting the data, of turning data from an accumulation of numbers into usable information. Not all numbers are the same. No group of people are all the same height, no group has an identical income, not all cars get the same gas mileage, not all manufactured parts are absolutely identical. How much do they differ? Variability is the key concept that statistics offers. It is possible to measure how much things are not alike. We use standard deviation, variance, range, interquartile range, and MAD (median absolute deviation from the median) as measures of not-the-sameness. When we compare groups we compare their variability as well as their range.