When I posted on DOEs, I briefly mentioned a statistical analysis package called Jump (JMP). I want to write more about that.
For some people, test engineering is about putting together the system. You build it, you ship it out to your customer (internal or external), and you move on to the next project. For others, test engineering is about managing the test process. The job revolves around SPC chores, preventive maintenance, & setting up new test runs.
But sometimes test engineering involves analyzing the results of the testing. I've spent plenty of time putting together graphs in Excel. But that sort of work can overload you when you have huge data sets & multiple sets of variables to consider. You need a more serious piece of software than just a spreadsheet for filtering down the data, looking at box plots, and plotting trends.
I know a guy who is a great statistician. He loves Minitab. The only package like that I've ever used is JMP, but he says it's a good piece of software as well. I know I like it, and more and more I've been using it instead of Excel when I need to examine data.
There are numerous books published by SAS (the company that wrote JMP) on how to use the software. I picked up one of them, Elementary Statistics Using JMP, and have read about half of it by skipping around to specific sections. The book is knowledgeable, well-organized and worth the money.