Historia Futura Praedicit where there is a fairly exhaustive analysis of some of the underlying data behind these graphs.
In 1987 Arthur Kellerman, a doctor who has done research on firearms and firearm related incidents, sent a survey asking if their was a firearm in the household to addresses that were listed in the firearm permit registries. His purpose, to see if those permit holders would respond truthfully. Of the 35 responses he received, 31 answered truthfully which would indicate that around 88% of gun owners would answer questionnaires honestly; however, what surprised him was that there were also 20 households that did not respond. When he went to investigate he found empty lots. In other words those permit holders had knowingly lifted a false address in order to keep their real home residence a secret from the authorities. If this polls is indeed accurate, then that means that 36% of those polled intentionally tried to hide the fact that they are gun owners. This sort of phenomena has repeated with the recent 'assault weapons' registration in Connecticut. Only around 11% of all estimated assault weapons holders registered their weapon by the deadline set forth in the law.This is rather a larger chunk than I would usually take for a quote, but the story is interesting to say the least. Dr Kellerman BTW is the source of the famous “43 times more likely” to be murdered in their own home if they own and keep a gun in their home" statistic which he has since reduced to 2.7 times more likely with added caveats about using drugs and other factors. Also no mention of the state in which the survey information was collected, but while most states do not have a registry of firearms owners, the ones that do are places where firearms owners are rightfully paranoid and would be reluctant to tell the Nosey Survey Company anything at all about their guns.
Click on over to the HFP link and read the whole thing. I found it interesting and it informs one as to where the Anti's are getting those bogus stories about the gun culture being in a serious decline. If 43% of gun owners will attempt to conceal their ownership of firearms that skews the ownership curves much higher than the 35-45% in the graphic above. What's in serious decline is trust in the government at any level at all and in anyone seen as a minion of said governments.