US mobile phone subscriptions per 100 people

Between 2005 and 2022, Californians and their trees produced ever-larger quantities of almonds while Americans simultaneously acquired more mobile phone subscriptions per capita, the two trends agreeing with each other at r = 0.9666 across 18 years. The obvious conclusion is that smartphones run on almonds, which would explain both the energy consumption and the slightly smug feeling one gets using them. The less obvious conclusion is that two unrelated things can grow together for nearly two decades without one causing the other, which is the sort of insight that statistical training is supposed to provide and rarely does.

California almond production grew from roughly 900 million pounds in 2005 to over 3 billion pounds by the late 2010s, driven by global demand—particularly from Asia and health-conscious Western markets—favorable economics for growers, and irrigation expansion. US mobile phone subscriptions per 100 people grew from about 68 in 2005 to near-saturation levels above 100 by the mid-2010s, tracking the smartphone revolution and network expansion. Both are driven by distinct forces—agricultural economics and telecom adoption curves—that happened to operate on similar timescales of secular growth.

Eighteen years is long enough that any two growing industries will produce a convincing-looking correlation. The almond does not know about the smartphone. The smartphone does not care about the almond. The data, regrettably, cannot tell the difference.