Clear flow charts can go a long way in explaining the randomization arms of your study or any other group allocation. There are 2 free options:

Desktop Programs

RFFlow is a free program “for drawing flowcharts, organization charts, and many other kinds of diagrams.” You can download a free demo version which does not expire but has a slight limitation on the number of figures in each chart (not a significant hurdle unless you plan to make very large diagrams).

Web-based Services

Gliffy is a web-based tool for flow chart design. Similar to the web word processor Writely, you can invite colleagues to collaborate on

a diagram. “Gliffy also stores multiple revisions of the same chart making tracking changes easier. You can even link your flowcharts from your blog or wiki”, writes the Digital Inspiration blog.

I used Gliffy to illustrate a post about DPP-4 Inhibitors for Treatment of Diabetes. The diagram is now on Wikipedia.

References:
Gliffy: Web-based Microsoft Visio - Google interested? Digital Inspiration blog.
Quick and simple online drawing. LifeHacker.com
Bubbl.us - Easy 2 Make Flow Diagram. Go2web2.
Create Animated Charts and Flash Graphs for your Website. Digital Inspiration, 2007.

Original post by Clinical Cases