Now that you have the requisite site and stats, you need to answer the first question of Habit Testing: “Who are the habitual users?” First, define what it means to be a devoted user. Ask yourself how often a user “should” use the site. That is to say, assuming that some day all the bugs are worked out and the product is perfectly “lickable,” how often would you expect a habitual user to be on the site?

Be realistic and honest. If your company builds a mobile social networking app like Foursquare or Instagram, you’d expect habitual users to be on the app several times per day.However, if you’re building a movie recommendation site, a la Flixster, you wouldn’t expect users to be on the site more than once or twice a week. Don’t come up with an overly aggressive prediction that only accounts for uber-addicts; you’re just looking for a realistic guess to calibrate how often users will interact with your site.

A good short-cut might be to take an average of how often you and the people in your office use your own product. Of course, more is better. Twitter was born within Odeo, the company Biz Stone and Jack Dorsey originally founded, because the engineers couldn’t stop playing with it.

One thing to note: the more frequently your product is used, the more likely it is to form a user habit. That’s not to say that web products that are used rarely can’t be good business, they just aren’t habit forming and thus have different characteristics. Viable, though non-habit forming businesses tend to be more transactional and require constant outreach to customers to stay top-of-mind.

For example, think of the travel industry’s relentless war to convince us to use one site over another. Expedia, Travelocity, and the rest, are used too infrequently by their average customers to form a habit, so they constantly compete for attention. These are viable, even profitable companies, but since they are non-habit forming products they are open to greater competitive threat. Products used daily naturally create barriers to entry in their markets.