Well, if you want to get REAL technical about it, you would need to base your statistical analysis not only on 1 out of 12 years of production, but also how many Broncos were built each year. Taking it even further, you should somehow try and account for how many of each year have been totaled, parted out, wrecked, or otherwise no longer on the road.
Figure all of this out, and get back to me with your updated answer :-*