Dediu's research on this topic was propelled forward when Apple CEO Tim Cook revealed the total number of active Apple devices -- 1.3 billion worldwide -- during the company's most recent earnings call. Now, the analyst proposed that to determine the average lifespan, you can subtract the known active devices number from cumulative devices sold to determine "cumulative retired devices."
Dediu then said that to estimate the average lifespan, you calculate the time between "cumulative devices sold" at the beginning of a product's lifespan, and the current "cumulative retired devices." He ultimately determined that the average Apple device lifespan is about 4 years and three months, when looking at the data of Apple products sold in Q2 2013 and retired in Q4 2017, a time when the 2013 devices died or otherwise stopped working and their owners sought to purchase new versions.
Dediu gave a detailed breakdown of his calculations:
Here’s how to compute this yourself: Visually, the lifespan is the distance horizontally between the two vertical bars such that the bars are the same length. The top vertical bar measures the gap between the area (cumulative devices) and the curve (active devices) and the lower bar is the gap between the area and the x-axis, i.e. the cumulative devices. When those two bars are the same size the distance between them is the lifespan (at the time of the top bar.)He noted that cumulative devices sold for Apple includes Macs, iPhones, iPads, Apple Watches, and the iPod touch, although of course the lifespan average number is just that -- an average -- and doesn't perfectly apply to each individual product. Just over four years is likely in the ballpark for how long Mac users keep around their computers, but if looked at on a product-by-product basis that statistic would likely be different for iPhone and Apple Watch owners.
Arithmetically, the average lifespan at a given time t is the duration between t and the moment when the cumulative devices sold reached the cumulative retired devices at time t.
For example today–as the visual above represents–the lifespan is the time since cumulative devices sold reached the current total retired devices. The cumulative retired devices can be calculated as 2.05 billion cumulative sold minus 1.3 billion active or 750 million. The time when cumulative devices sold reached 750 million was the third quarter 2013. The lifespan is thus estimated at the time between now and Q3 2013 or 17 quarters or about 4 years and three months.
For more details on the topic, check out Dediu's full post on Asymco.com.
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