The qplot (quick plot) system is a subset of the ggplot2 (grammar of graphics) package which you can use to create nice graphs. It is great for creating graphs of categorical data, because you can map symbol colour, size and shape to the levels of your categorical variable. To use qplot first install ggplot2 as follows..

Data analysts can get away without ever understanding matrix algebra, certainly. But there are times when having even a basic understanding of how matrix algebra works and what it has to do with data can really make your analyses make a little more sense.

In Part 20, let’s see how to create mathematical expressions for your graph. Mathematical expressions on graphs are made possible through expression(paste()) and substitute()...

Today we see how to set up multiple graphs on the same page. We use the syntax par(mfrow=(A,B))..

Time Series are economic or other data that are collected over an extended period of time. Many clever methods have been developed to analyze time series, both to understand the factors that cause variation and to forecast future values.

One of those “rules” about statistics you often hear is that you can’t interpret a main effect in the presence of an interaction. Stats professors seem particularly good at drilling this into students’ brains. Unfortunately, it’s not true. At least not always.

You may have heard of McNemar tests as a repeated measures version of a chi-square test of independence. This is basically true, and I wanted to show you how these two tests differ and what exactly, each one is testing.

On my first assignment using Stata, I think I spent four or five hours trying to present my output in a “professional” form. The most creative method I heard about in class the next day was to copy the contents into Excel, create page breaks and then copy into Word. SPSS makes it so easy to copy tables and graphs into another document. Why can’t Stata be easy? Anyone who has used Stata has gone through this and many of you still are. No worries, help is on the way!..

We've already discussed using macros in Stata to simplify and shorten code. Another great tool in your coding tool belt is loops. Loops allow you to run the same command for several variables at one time without having to write separate code for each variable. This discussion could go on for pages and pages because there is much you can do with a loop...

We finished the last blog with the confusing coding of: local continuous educatexper wage age foreachvar in `continuous'{ graph box `var', saving(`var',replace) } I admit it looks like a foreign language. Let me explain how simple it is to understand..