According to Oakland County, Mich., authorities, James Crumbley bought a Christmas present last Friday. It was Black Friday, a day on which Americans commonly begin shopping for the holidays in earnest. Crumbley’s alleged purchase was one that’s also common these days: a handgun, intended as a gift for the son who joined him at Acme Shooting Goods when the purchase was made.

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       On this particular Black Friday, nearly 188,000 instant background checks were conducted through the FBI, generally (but not always) indicating the purchase of a new firearm. Since the instant background check system was implemented in 1998, there have been only nine days on which more background checks were conducted.

       In the case of James Crumbley, we see one of the flaws in that system. According to the county, his son brought the gun to school Tuesday, where he allegedly used it to kill four of his classmates. That James Crumbley seems to have passed a background check did not prevent the weapon from allegedly being used in a violent crime. Crumbley and his wife now face criminal charges related to the shooting.

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       In the past, the FBI only shared data on background checks on a monthly basis. Recently, though, they’ve expanded that, creating a file that indicates the number of background checks conducted on any day since the system was put in place. That allows us a unique opportunity to see the patterns in gun sales, using background checks as a proxy.

       We took that data and created a visualization of sales by day since Nov. 30, 1998. Each day is indicated with a square. The darker the red that square is colored, the more background checks were completed. Squares outlined with white boxes are days on which a record number of background checks were performed. We’ve also added notes to indicate various patterns and anomalies.

       As noted in the graphic, the number of background checks has increased over time. We can visualize that another way. Here, for example, is the number of background checks each year as a function of the country’s population. Two decades ago, there were about 30 checks for every 1,000 Americans each year. In 2020, the figure was four times as high.

       Again, this is not only because of more gun sales. Some states use background checks for permitting, for example; in some states, those checks occur multiple times a year.

       But it is also because of increased gun sales.