Drawbacks: Because it's trying to ignore words such as "a" and "the," the basic configuration can miss some important terms. In my tests, it didn't know the difference between "it" and "IT," and completely missed "AT&T."
Skill level: Advanced beginner. This app runs on the command line, so users should have ability to find file paths and plug them into a sample command.
Runs on: Windows, Mac OS X and Linux running Java.
Learn more: Check the examples that come with the download.
Social and other network analysis
These tools use a pre-Facebook/Twitter definition of "social network analysis" (SNA), referring to the discipline of finding connections between people based on various data sets. Investigative journalists have used such tools to, for example, find links between people who are involved in development projects or who are members of various boards of directors.
An understanding of statistical theories of network node analysis is necessary in order to use this category of software. Since I've only had a very basic introduction to that discipline, this is one category of tools I did not test hands-on. But if you're seeking software to do such analysis, one of these might meet your needs.
What it does: Billed as a Photoshop for data, this open-source beta project is designed for visualizing statistical information, including relationships within networks of up to 50,000 nodes and half a million edges (connections or relationships) as well as network analyses of factors such as "betweenness," closeness and clustering coefficient.
Runs on: Windows, Linux, Mac OS X running Java 1.6.
Learn more: Try this Quick Start tutorial (PDF).
What it does: This Excel plug-in displays network graphs from a given list of connections, helping you analyze and see patterns and relationships in the data.
NodeXL merges the older and current definitions of SNA. It's "optimized for analyzing online social media -- it includes built-in connections to query the APIs of Twitter, Flickr and YouTube, allowing you to draw networks of users and their activity," according to Peter Aldhous, San Francisco bureau chief for New Scientist magazine.
It also handles e-mail and conventional network analysis files (including data created by the popular -- but not free -- analysis tool UCINET).
Runs on: Excel 2007 and 2010 on Windows.
Learn more: Download this detailed free NodeXL tutorial (PDF) or these basic step-by-step instructions on analyzing your own Facebook social network (PDF). One Facebook app for downloading your own friend information for use in NodeXL is Name Gen Web.
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