Sign-of-the-times stats on eve of the conventions

A look at the U.S, past and present, by the numbers:

LEAPS AND BOUNDS: The U.S. population has more than doubled since Mitt Romney was born in 1947. Population then: 144.1 million. In 1961, when Barack Obama was born: 183.7 million. This year: 314 million. The U.S. grows by one person every 12 seconds.

LIVING LONGER: Life expectancy has reached 78.5 years, up from 66.8 when Romney was born and 70.2 when Obama was born. The average person lives six years longer in Japan, one of 49 countries with longer life expectancy.

HEATING UP: The coldest yearly national average temperature, in records going back to 1895, was 50.82 degrees in 1917. Hottest year on record was 1998, at 55.08 degrees. The July 2011-June 2012 period was the hottest 12-month stretch on record: 56 degrees, 3.2 degrees above the long-term average.

SAME-SEX MARRIAGE: On May 17, 2004, dozens of same-sex couples in Massachusetts took vows to become “partners for life” as the state became the first to recognize gay marriage despite opposition by Romney, then governor. It has since become legal as well in Connecticut, Iowa, New Hampshire, Vermont, New York and the District of Columbia. Thirty-one states have passed measures aimed at banning gay marriage.

DIFFERENT-RACE MARRIAGE: More than 15 percent of new marriages were interracial in 2010, Pew researchers found. In all, an estimated 8.4 percent of all marriages are between races, up from only 3.2 percent in 1980. The trend is especially strong in the West, with the South next despite its long history of segregation, followed by the Northeast and Midwest.

WARS RECEDE: The U.S. had 67,700 troops in Iraq in 2003, 157,800 in 2008, none now. In Afghanistan, the U.S. had 10,400 troops deployed in 2003, 30,100 in 2008 and 88,000 in June 2012. Altogether, about 100,000 fewer troops are engaged in the conflicts abroad. The numbers deployed in Afghanistan surpassed the force in Iraq for the first time in June 2010 — 94,000 compared with 92,000.

EFFECTS LINGER: In the first five months of this year, suicides of active-duty troops (154) far outnumbered forces killed in action. On a single night in January, an estimated 67,495 homeless veterans were on the street in 2011, 76,329 in 2010 and 75,609 in 2009.

THAT NUMBER: The unemployment rate, the most politically sensitive digits around, stands at 8.3 percent. It’s been above 8 percent since February 2009 and peaked at 10 percent in October 2009.

HOME SWEET & SOUR HOME: The rate of home ownership peaked at 69.2 percent in late 2004, highest on record dating to 1965, dropping early this year to 65.4 percent, lowest since 1997, ticking up since to 65.5 percent. The rate refers to the percentage of households that are owner-occupied. Meantime the average home size in 2010 was 2,392 square feet (a basic two-car garage is 400 square feet), down 5 percent over three years. Builders broke ground on nearly 2.1 million homes and apartments in 2005, the most since 1972. That number fell to 554,000 in 2009. It is on pace to rebound to 750,000 this year. Economists say housing starts of about 1.5 million are what you’d expect in a healthy economy.

THE WEIGHT OF PLASTIC: Credit card debt has dropped 14 percent since 2008.

PENNIES SAVED: The savings rate climbed to 4.2 percent last year, a big increase from 1.5 percent in 2005.

ROAD GAUGE: The average commuter wasted 14 hours stuck in traffic in 1982, 39 hours in 2005 and 34 hours in 2010, says the Texas Transportation Institute.

GAS GAUGE: 91 cents for a gallon of regular in 1999, rising to $2 in May 2004, $4 in June 2008, plunging to $1.61 by that Christmas. This year’s peak: $3.94.

CHARITY: Fewer Americans are sharing their time and talents as volunteers in communities, but they’re opening their wallets a little more. The number of adults volunteering peaked at 65 million in 2005. It then dropped to just below 63 million five years later. Charitable giving, however, rose ever so slightly with people, businesses and foundations giving almost $291 billion in 2010. That’s up following declines in the two previous years, the biggest drops in giving in more than 40 years as a result of the recession.

GREENERY: The U.S. has 751 million acres of forest land — one-third of the total land area. That’s been stable since the beginning of the 1900s. Building in cities and elsewhere has been offset by trees growing back in other areas.

LINGO: “Occupy” was voted 2011 word of the year by the American Dialect Society, thanks to Occupy Wall Street and related protests. The sign-of-the-times winners of past years: “app” in 2010, “tweet” in 2009 and the no-fun “bailout” in 2008. Word of the past decade: “google” as a verb. A 2011 finalist for most creative word: “kardash,” a unit of measurement consisting of 72 days, inspired by the brief marriage that year of Kim Kardashian and Kris Humphries.