stats on tv

I just saw a Toyota ad on tv that claimed that 80% of Toyota vehicles sold in the last 20 years are on the road today. What this statement would like you to believe is that if you buy a Toyota now, chances are good that it will be drivable for 20 years.

What the statement actually tells you is that of the cars sold over the period 1989-2009, 80% of those cars are on the road today. However, the distribution of "hard" failures is unknown, at least just from these statistics. It could be the case that all Toyota vehicles fail at exactly the 16-year mark: if Toyota sells the same number of cars each year, then the cars that would be running today were sold between 1993 and 2009, or 16 years worth (80%) of cars.

Alternatively, it is highly likely that the number of Toyota cars being sold today is much higher than it was in 1989, so of those 80% that are running today, most might have been sold in the last 10 years or so, which might put the average lifespan closer to the early teens.