These are the facts. The U.S. population did not grow that way, not even approximately. That is a fact. It is also a fact that the average number of classmates a student will find in his or her classes is 37. That too is a fact.
Musicians begin with their scales.
Data analysts begin with lines and tables. So, for example, the line constructed on the graph in Figure 1 expresses a hypothetical relation between education, left to right, and income, bottom to top. This first idea, the straight line, is the best tool that data analysts have for figuring out how things work. The first idea, the line, is reserved for data we can plot on a graph, while this second idea, the additive model, is used for data we organize in tables. Adding it up, Observed equals All Effect plus Phoenix Effect plus July Effect plus Residual .