Scattergrams and Plotting Lines and Graphs.
Morrison on Metrics: Grouped thoughts on scattergrams
The finer points of plotting graphs and lines
Rees Morrison, InsideCounsel
When you create a scattergram, the most common additional step of analysis and visualization is to superimpose on it a trend-line. If you use the default trend-line function of Excel, the line will be straight (known as the least squares line), and it will generate an equation for the line. A straight line, however, may convey a distorted sense of the trend of the points on a scattergram that has some unusually high or low numbers or anomalies in the middle of fairly consistent numbers. (read the post)