Pictures can tell a lot. In fact, a single image can be packed with information. For example, this satellite image of the United States taken at night can tell us a lot. This image shows us major urban areas. It also shows us the outlines of major natural features like Lake Michigan, and it also illustrates how the eastern half of our country is more densely populated compared to the western half.
While today's world is full of images, statisticians have long known the value of summarizing large data sets with pictures. Some great examples are found in Edward Tufte’s book, The Visual Display of Quantitative Information. One of the best examples of this actually comes from Nursing. Florence Nightingale’s descriptive pictures of mortality statistics illustrated how soldiers, even in peacetime, faced twice the risk of dying compared to civilians. Her descriptions helped make the case for improved sanitary conditions for soldiers' living quarters.
This week we will start by showing you how frequency distribution and histograms can be used to summarize large data sets. Next we will illustrate how several simple statistics can summarize both the center and the spread of distributions.