Many of our user experience consulting clients often ask us if they can or should moderate usability tests sitting next to the user. The most common questions include:
1. Can I sit next to the user during usability testing? Yes, absolutely. Though there is no methodology rule for sitting next to the user during the test. The reason you would sit next to them is to provide more intimacy, or "hands on" moderation. In other words to make the user feel more comfortable.
2. Do I have to sit next to the user during the usability test? Not necessarily. Our usability labs are designed so that you do not have to sit next the user if you choose not to. This is really a moderator preference. We find it is easier to use our intercom system to communicate with the user, leaving them to work alone on their tasks. There is less chance of moderator stress or participant bias this way.
3. What benefit is there from being next to the user vs. being behind the one-way mirror? The one-way mirror (or located in another room is another common configuration with our usability lab) is valuable because it gives moderators space to log notes or observe, comment and do their own thinking out loud! On the flip side, the benefit of sitting chair side is increased intimacy or what in the UK nursing profession is called "bedside manner". It will depend on what kind of test and what type of user you are dealing with.
When I first started moderating usability tests 15 years ago, I used to almost always sit next to the user. I used to think it added better moderator observation. The more usability testing I conducted, the more I found it awkward to take notes and/or observe so close to the user. These days I find it easier to moderate using our usability lab's intercom system (you cab also can create a link with walkie-talkies or a conference call bridge). Sometimes if I feel the user is anxious, I will sit chair-side. For accessibility testing, I always sit beside the user.
The bottom line, is there is no rule, it is up to you and depends on what usability lab set up you have or how close you prefer to get to your users.