US mobile phone subscriptions per 100 people

Over twenty-one years, from 2002 to 2022, the number of IRS individual tax returns e-filed and US mobile phone subscriptions per 100 people grew together at r = 0.9658. This is one of those correlations that is accidentally measuring something real: both are proxies for digital adoption. The American who got a smartphone in 2008 is the same American who stopped mailing paper tax returns in 2009, and the data knows it, even if the IRS and Verizon have never coordinated their growth strategies. The correlation is spurious in name but genuine in mechanism—the rarest and most uncomfortable category on this website.

IRS e-filing grew from roughly 47 million returns in 2002 to over 150 million by 2022, driven by IRS Free File programs, TurboTax and H&R Block digital platforms, and mandated e-filing requirements for preparers. Mobile subscriptions per 100 people grew from about 49 in 2002 to above 100 by the mid-2010s, tracking smartphone adoption and network expansion. Both are digital adoption S-curves across the same two-decade window, driven by the same underlying shift: American consumers moving from analog to digital processes across every domain of their lives.

Occasionally a spurious correlation accidentally captures a real phenomenon. Digital adoption drove both e-filing and mobile subscriptions, making this correlation less spurious and more just poorly attributed—the variables are different measurements of the same transformation.