UCLA Statistics has a pretty extensive list of resources on how to use R and GRASS. For those unfamiliar, R is a programming language and environment for statistical computing and graphics. GRASS is an open source geographic information system (GIS). And of course, both are completely free and completely useful.
Useful Stat Resources for R and GRASS
Graphical perception – learn the fundamentals first
Before you dive into the advanced stuff – like just about everything in your life – you have to learn the fundamentals before you know when you can break the rules.
People get married at various ages, but there are definite trends that vary across demographic groups. What do these trends look like?