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@@ -15,6 +15,23 @@ knitr::opts_chunk$set(collapse = TRUE)
 
 Excerpt from the [Gapminder](http://www.gapminder.org/data/) data. This R data package provides the data as a data.frame and in plain text delimited form. Package includes premade color schemes for the countries and continents.
 
+This data.frame includes six columns, ([documentation page here](http://www.gapminder.org/data/documentation/gd001/)):
+
+| column name | meaning         | 
+|:------------|:----------------|
+|country      | country name    | 
+|continent    | contient name   |
+|year         |                 |
+|lifeExp      | Life Expectancy |
+|pop          | Population      |
+|gdpPercap    | per-capita GDP  |
+
+Per-capita GDP (Gross domestic product) is given in units of [international dollars](http://en.wikipedia.org/wiki/Geary%E2%80%93Khamis_dollar). From Wikipedia:
+
+> [...] the international dollar is a hypothetical unit of currency that has the same purchasing power parity that the U.S. dollar had in the United States at a given point in time
+
+In gapminder, the currency matches the US dollar in 2005.
+
 ### Install and test drive
 
 Install `gapminder` from CRAN: