Coding for Applied Economists

Density Functions (Graphing)

Using the nlsw88 data,

1. Draw a kernel density of total work experience.

2. Draw a version with less smoothing.

3. Draw a version with more smoothing.

Stata can overlay a normal density curve with the same mean and variance as your data on top of the kernel density estimate. This lets you visually compare your distribution to a smooth, bell-shaped curve (we are not doing formal hypothesis tests here).

4. Draw a kernel density of ttl_exp using the normal option.

5. Finally, we will put it all together by drawing a histogram and a kernel density for ttl_exp on the same plot and make the graph presentation-quality.

  • First, choose reasonable binning (20) for ttl_exp and draw a histogram with percent on the y-axis:
  • Next create a combined graph with both the histogram and the kernel density. Use twoway to overlay them:
  • Modify the graph by adding the color(%60) option, which makes the bars lighter (60% of full opacity) so the density line stands out.
  • Change the title() of the graph to be “Distribution of total work experience”
  • Change the x-axis title to “Total work experience (years)” and the y-axis title to “Percent of workers”
  • Finally, create a legend and place it below the graph (pos) and in two columns (col). Label the shaded area using 1 "Histogram" and the line using 2 "Kernel density".