While writing Sunday's story on a surge in gun and ammunition sales, just posted online, I ran into contrasting survey results about gun ownership in the United States.

One longstanding, respected survey says the number of households where residents have at least one gun has been declining almost continuously since the late 1970s. This one, the General Social Survey by the National Opinion Research Center at the University of Chicago, says that as of 2010, 32.3 percent of Americans reported having a gun in the home.

Another longstanding, respected survey says gun ownership has risen and fallen for years but not shown a steady decline, staying largely in the 40 percent to 50 percent range for decades. This one, by Gallup, says gun ownership soared from 2010 to 2011, jumping from 41 percent to 47 percent of U.S. households in that time.

Not surprisingly, advocates for stricter gun laws tend to cite the former survey, suggesting that gun dealers must sell more guns to a declining portion of the U.S. population. (See attached Violence Policy Center report.)

Gun-rights advocates tend to cite the latter poll, explaining that a greater portion of Americans appear to be exercising their 2nd Amendment rights.

I talked (or emailed) with representatives of both surveying groups this morning, trying to suss out what explains the different results. Both polls have been done for decades and ask similar questions amid broader surveys.

Gallup asks "Do you have a gun in your home?" And if you say no, they ask if you have one elsewhere on your property, such as a garage, barn, shed, car or truck.

The General Social Survey asks “Do you happen to have in your home any guns or revolvers?" A follow-up asks about whether there is a gun in the garage.

Frank Newport, the editor in chief of Gallup, emphasized that their survey has asked their gun question consistently, in the same context, for decades. The question is part of a broader survey on crime, violence and guns, taken every October.

He said it's unclear whether the six-percentage-point uptick shown in last year's poll will prove to be anomalous.

I also asked Tom Smith, director of the General Social Survey, about that increase shown in the Gallup survey from 2010 to 2011. He said it was unlikely to be correct and explained his opinion this way in an email:

"What that literally would mean is that in one year at least 6.9 million guns were added to households that previously had no firearms (and that no households that had guns got rid of all of their firearms during the same period). If the new gun owning households acquired more than the minimum one gun per household that would require even more guns. If it was 1.1 guns per household, then it would total about 7.6 million guns being added to households previously without firearms"

"The 2009 and 2010 [NICS] background check figures were both about 14 million (and lower in other recent years). Those levels of background checks were associated with no increase in the % of households with guns according to Gallup. In 2011 the level was up to about 16.5 million. While that gain of 2-2.5 million background checks, could indicate more guns going to new households, it doesn’t suggest that 7.6 million guns went to new gun owning households."

Long story short, Smith says a six percentage point increase would require a tremendous increase in the number of households where people obtained their first gun, something that's not supported by FBI background-check data.

There are, of course, other sources of data, but most of them have an interest in the results. For example, the National Shooting Sports Foundation, a firearms-industry group, does an annual survey of firearms retailers