Two other graphic methods are useful in univariate analysis: histograms and frequency polygons. Frequency polygons are line drawings made by connecting the tops of the bars of a histogram and displaying the result without the bars. What you get with both graphs is pure shape—less information than you get with box plots or stem-and- leaf plots but easily interpreted. Figure 20.6 shows the histograms and frequency polygons for TFR, MFRATIO, and PCGDP.

These visualizations for MFRATIO nail down what we know from the box-plot of that variable: Most countries are in a narrow range, but a few are real outliers. The histogram/ polygon for PCGDP removes all doubt about the shape of this variable: It is skewed to the right, with most countries at the bottom and a long tail of countries to the right.

And we can now see that the variable TFR is distributed bimodally. Countries across the world tend to have either low TFR (22 have a TFR of 2 or below) or high TFR (18 have a TFR of 3 and up), with just 10 countries in the middle range, between 2 and 3.