John Wilkins has an excellent exposition on belief at Evolving Thoughts
... it's woven into a multipart series, the relevant post here is Atheism, agnosticism and theism 2: What it is to have a belief
If beliefs are "maps by which we steer" ( Frank Ramsey ) - then I find it useful to assign a level of confidence to each map (or belief) that I steer by. For instance, I believe the sun will come up tomorrow. I'm sure, in fact, that the sun will come up every day of my life. Assuming that I will live for 100 years (just because it's easy to calculate, not because it's reasonable) - I expect that every one of those 36,525 days there will be a sunrise. So, I might say that I'm 36525/36525ths sure. Assuming - like a reasonable person, that something might go wrong and the sun doesn't come up one day, how do I express that in terms of a whole lifetime? .99997 happens to be the number - once in 36,525 days - or 99.997% of the time I expect the sun to come up. Now, I don't actually expect that to ever happen, but as a measure of certainty, 99.997% is a figure that I can relate to - something real in this life.
There are some affirming facts, and some independent non-scientific confirmations to attest to at least this level of certainty. First, the Earth revolves on its axis at the rate of 365.25 times per year. Second, the Earth has enough mass to continue at this speed with negligible degradation for thousands (millions!) of years; third, the mass of the Earth, the mass of the Sun, and the orbital speed of the Earth around the Sun indicate that the Earth-Sun relationship will remain relatively constant for thousands (millions) of years; fourth, there are no imminent significant physical threats that would alter the first three facts.
As for anecdotal confirmation - approximately seven billion people can attest to a sunrise occurring this morning. Going back through the history of man, there may be 50-100 billion folks that we consider human, all of whom can attest to the consistently occurring sunrise, without a single credible exception. These personal attestations are not the core of the argument - but they are consistent to a degree not usually found in other areas of belief - billions of people, tens of thousands of days each, without exception.
What are the chances that there is something supernatural in the world - or, getting to the point - that there is a "god" that is the creator, supervisor, omniscient, omnipotent intervener in the lives of only certain people and not others?
First, look at the evidence.
Second, assign a certainty.