It began with a simple question.

Why are we able to get information about so many subjects so easily, yet not about the most vital and interesting subject: the probabilities of everyday life?

If we wish to understand the meaning of a word we use a dictionary. To understand its connotations we refer to a thesaurus. The history of the word? The glorious Oxford English Dictionary. Find a website? Go to the great search engines. Find out more about a subject? The encyclopedias, wiki and print. But when we wish to know what a probability means, where do we go?

The world needed a book of odds.

Well, not a book, exactly. A flexible, updatable, memorable way to gain new insights into the world thanks to the world of data humanity has created. A BookofOdds.com.

Could it be done? Early in 2006, I ran an informal test. Working with two students, one from Harvard, and one from M.I.T., we created the first instance of the “Book of Odds.” It was a hand-made operation, each Odds Statement—450 of them—crafted individually. This list hangs on our office walls, imperfect but full of promise, like a photo of a beaming gap-toothed child.

Three things made this first list unique. It covered subjects unrelated to each other. It put the Odds Statements in a common, standardized format, no matter the subject. It arrayed the statements in order of probability not by topic.

It began with very high probability. The odds a death row inmate is a man, we found, are 1 in 1.02 (US, 2005) and the odds a person who dies from a bicycle accident in a year is not wearing a helmet are 1 in 1.05 (US, 1995). When one thinks about it there aren’t many women given death sentences, and fewer actually executed, only 11 in that last 32 years. That virtually only helmetless riders run risk of death— or used to, since helmeted death rates began to increase in 1999—is sobering in the light of the first Odds Statement. I began tightening my chin strap.

Other accidental pairings shed light on distressing facts. Take this one: “The odds a female who is raped is under 12 are 1 in 3.45 (US, 2004).” That is shocking in and of itself, but it is made more vividly awful when one looks for another Odds Statement in the same range. “The odds a man over 100 will die in a year are 1 in 3.56 (US, 2002)” The odds a female rape victim is under 12 are about the same as a 100-year-old man dying in the next 12 months.

By placing similar odds beside each other without regard to their content, the juxtaposition sheds light for a reader with familiarity with any of the subjects. It was now possible to look up topical matters such as the odds of this disease or that crime and so forth. It was also possible to look up the probability number itself and find something one can relate to.

I showed this original list to many people in the early years of developing Book of Odds. Not a person failed to be fascinated or to be surprised or make personal connections. Since these were people from all walks of life and interests, I knew that the subject really was of wide interest. Moreover, many of these people were not mathematically inclined. One, a respected novelist, was so biased towards words over numbers that her English SAT’s got her into Stanford while her math SAT’s suggested the salt mines. She found the list irresistible and said so, volubly and many times.

If a mere 450 Odds Statements could be revealing and fascinating, what would it take to make 1,000 times that number and more? It would be hard, surely, and there would be many challenges associated with scaling up to the level of a true reference source, but the first experiment had answered one question decisively: it was worth doing.

So it was worth doing well, as the saying goes. I found a brilliant and indispensible colleague in Louise Firth Campbell. Students and graduates from some of the top universities in the country joined us to do research and develop the technical solutions needed to manage information derived from so many disparate sources. As with any reference source we had to develop conventions for thousands of matters, from tense to terminology. We had to put some boundaries on the scope of the first public effort. These included selecting the topics we thought most interesting and leaving some for our continuing update and expansion efforts. It also meant focusing first on the US, the amazingly interesting cross-country comparisons to be part of our expanding database.

Three years after the first list of 450 was created we launched BookofOdds.com, only now with over 250,000 odds statements and more pouring in. We weren’t perfect in our first incarnation and we don’t suppose we are now. We have been careful though, and thoughtful, and stayed true to our mission to provide the means to understand the probabilities of everyday life.