Visualizing Patterns over Time - Data Points: Visualization That Means Something - page 128

FIGurE 4-46 Fitting a line to data points

LOeSS starts at the beginning of the data and takes small slices. At
each slice it estimates a low-degree polynomial for just the data in the
slice. LOeSS moves along the data, fitting a bunch of tiny curves, and
together they form a single curve. You can Google it for more details.
There are several papers on the topic. Now get into how to use LOeSS
with your data.

P See “Robust
Locally Weight-
ed Regression
and Smoothing
Scatterplots” in
the Journal of the
American Statisti-
cal Association by
William Cleveland
for full details on
LOESS.

FIT A LoESS CurVE
The story you look at is unemployment in the United States over the past
few decades. There have been ups and downs, along with seasonal fluc-
tuations. What is the extent of the overall trends? As shown in Figure 4-47,
the unemployment rate peaked in the 1980s, declined through the 1990s,
and then shot up around 2008.