Graphs for panel data"Stata 9 introduced the xtline command. Xtline allows you to generate linear plots for panel data. We will show a number of examples from a data file which contains a measurement of alcohol use, alcuse, taken at ages 14, 15, and 16 for 82 children (identified by the variable id). We use Stata graph scheme s2mono, which produces plots in grayscale, because publications often require monochromatic plots."