Silver was born in East Lansing, Michigan, the son of Sally (nee Thrun), a community activist, and Brian David Silver, a former chair of the political science department at Michigan State University. Silver's mother's family, of English and German descent, includes several distinguished men and women, including his maternal great-grandfather, Harmon Lewis, who was president of the Alcoa Steamship Company, Inc. Silver has described himself as "half-Jewish". Silver showed a proficiency in math from a young age.

On November 1, 2007, while still employed by Baseball Prospectus, Silver began publishing a diary under the pseudonym "Poblano" on the progressive political blog Daily Kos. Silver set out to analyze quantitative aspects of the political game to enlighten a broader audience. Silver reports that "he was stranded in a New Orleans airport when the idea of FiveThirtyEight.com came to him. 'I was just frustrated with the analysis. ... I saw a lot of discussion about strategy that was not all that sophisticated, especially when it came to quantitative things like polls and demographics'". His forecasts of the 2008 United States presidential primary elections drew a lot of attention, including being cited by The New York Times Op-Ed columnist William Kristol.  On March 7, 2008, while still writing as "Poblano," Silver established his own blog, FiveThirtyEight.com. Often colloquially referred to as just 538, the website takes its name from the number of electors in the United States electoral college.  On May 30, 2008, Poblano revealed his identity to FiveThirtyEight.com readers. On June 1, 2008, Silver published a two-page Op-Ed article in the New York Post outlining the rationale underlying his focus on the statistical aspects of politics. He first appeared on national television on CNN's American Morning on June 13, 2008.  Silver described his partisan orientation as follows in the FAQ on his website: "My state [Illinois] has non-partisan registration, so I am not registered as anything. I vote for Democratic candidates the majority of the time (though by no means always). This year, I have been a supporter of Barack Obama". With respect to the impartiality of his electoral projections, Silver stated, "Are [my] results biased toward [my] preferred candidates? I hope not, but that is for you to decide. I have tried to disclose as much about my methodology as possible".

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