One in four adults in California lives in a household with a gun, including around 1 in 7 (14%) who personally own a firearm, suggest the results of a survey published in the journal Injury Prevention.
This equates to an estimated 7.3 million residents, state-wide, calculate the researchers.
In 2017, nearly 40,000 people died from firearm injuries in the USA, the highest number in more than two decades. A gun in the household increases the risk of firearm death and injury, particularly unintentional shootings, suicide, and murder (of women), the evidence shows.
California has a relatively low rate of firearm deaths per person, but ranks second in the US for overall firearm violence, with a total of 3083 such deaths in 2017, half of which were suicides.
The latest estimates of firearm ownership for each state are more than 10 years old, while detailed information on the number and type of gun each person owns, and the reasons why, hasn't been collected in more than 40 years, say the researchers.
To plug this knowledge gap, they analysed the responses of 2558 adults to the California Safety and Wellbeing Survey on firearm ownership in September-October 2018 (49% response rate).
One in four (just under 25%) respondents said either they (429; 14%) or someone else (242; 11%) in their household owned one or more firearms.
If those figures are applied to all of California's adult residents, it means 4.2 million people own a gun in the state, while another 3.1 million live in a household with someone else who owns a gun, estimate the researchers.
The average number of firearms among owners was around 5, adding up to a collective tally of 19.9 million state-wide, they calculate.
While more than half (54%) of the gun owners said they owned just 1 or 2, one in 10 said they owned 10 or more, accounting for nearly half of all the guns in the state.
Most firearm owners (56.5%) said they were the only person in the household to own a gun; one in three (33%) said they lived with one other owner. And one in 10 said they lived with two or more other owners, including spouses or partners (64%).
Most owners were aged at least 60 (43%); male (73%); and white (64%). Seven out of 10 grew up in a household with a firearm.
Just over half (55%) of all firearms in the state were long guns (mostly rifles), although handguns were the type of firearm last acquired (56%).
More than two thirds of owners (69.5%) said they had bought their last firearm, with the remainder (30.5%) saying they had either inherited theirs (54.5%) or been given it as a gift (28%).
Most purchases (86%) were made from a retailer, such as a gun store, sporting goods store, or pawnbrokers.
Reasons for ownership varied by gun type, with more than half (57%) of handgun owners saying this was mainly for protection against people, while sport and hunting were the main reasons given for owning a long gun.
This is an observational study, and as such, can't establish cause. The total sample size was relatively small and no information was available for those who didn't respond to the survey, the researchers point out.
But they suggest: "These findings may signal a shift in the underlying drivers of contemporary firearm ownership from participation in hunting and other recreational activities to a perceived need for self-protection, similar to patterns observed on a national level.
"And [they] suggest that efforts aimed at reducing firearm death and injury may need to address self-protection as a primary driver of ownership, along with misconceptions about the benefits of having a firearm in the home."
Peer reviewed: Yes
Evidence type: Observational; survey data