Horace Dediu is on a roll.
From Asymco: Determining The Average Apple Device Lifespan
In The Number I provided a model for estimating the number of active Apple devices at any point in time. The relationship between active devices and cumulative devices sold gives us a rule of thumb that says that 2 out of 3 devices ever sold are active.
I propose now that knowing active devices and cumulative devices sold allows one to determine the average device lifespan.
See below for the graphs he uses to represent his methodology.
The lifespan is thus estimated at the time between now and Q3 2013 or 17 quarters or about 4 years and three months. (emphasis mine)
I’ll show in the next post how this single number allows us to calculate the net present value of Apple’s future cash flows, or, by definition, Apple’s enterprise value.
My take: Can't wait to see how Dediu's calculation of Apple's enterprise value compares with, say, Yahoo's estimate ($953.34 billion.).