Yes - You Need a Full Time Scrum Master

Many organizations adopting Scrum ask these questions.

• Do we need a full time Scrum master for each team?
• Why do we need a full time Scrum master, can't they do other roles also?

Now allow me to give you the answers: 

• Yes, you need a full time Scrum Master.
• Why - watch the video.

Let me explain:

Yes, you need a full time Scrum master, because they will be constantly watching for the actions of the team.  Making sure that the team member are working in flow as often as possible.  This is a full time job.

Why can the scrum master not do other roles on the team? Because of the human ability of selective attention.  First let me show you a video - a little test of your superior ability to follow instructions.  Perhaps you've seen this video - if so, just play along, maybe you will be surprised at how well you do on the test.

The Monkey Business Illusion

Now do you understand why we need a Scrum master watchhttp://www.infoq.com/articles/case-dedicated-scrum-mastering out for impediments all the time.  If they are tasked with doing something else, I'm sure they will miss the obvious impediments the subtle changes in the team members and the environment.

Here is Jeff Sutherland's reasoning (from Scrum Development Yahoo group):

"One of the leading Agile teams in software development asked me how to go hyperproductive. I was their coach as my venture group had invested in them. They had a fuzzy ScrumMaster definition and it was not clear who owned this role. I told them to get a ScrumMaster. The experienced team thought they were better than that and could never go hyperproductive. A new team was formed with a ScrumMaster which immediately went hyperproductive."

"So a lot of teams that think they don't need a ScrumMaster are a long way from 10 times the performance of a waterfall team. This was the design goal for Scrum and every team should be getting a 10% velocity increase sprint to sprint until they hit that number."

"Teams without ScrumMaster's don't do this. Usually they are flatlined and will never reach their full potential."

  --  Jeff Sutherland

See Also:
Can you Use a ScrumMaster - Bob Marshall
Is ScrumMaster Really a Full Time Job? - David Hawks
30 Reasons why a Part-Time Scrum Master is not Optimal by Luis Goncalves

Have you heard of the Fleas in the Jar Experiment - watch the video:

Where should Scrum Masters report? - Ryan Dorrell
An analytical approach to the same question:  Scrum Master Allocation: The Case for a Dedicated Scrum Master  by  Melinda Stelzer Jacobson on InfoQ
Can you use a Scrum Master by Bob Marshall the FlowchainSensei
The Scrum Master as the Change Leader by Barry Overeem