Now believe me when I tell you this as I was in Detroit often (throughout my near 50 years) and experienced the ups and downs of this process, first hand. I lived through some good times and some bad times , there. As suggested in the graph above, times just didn't get bad, stay at that point for awhile and then get worse (suggesting a staircase effect). No, there were bad times of decline that were followed by the good times of incline that lead to times of even further decline (suggesting somekind of saw tooth or triangular effect), downwards.
Back to the population graph, it's suggesting that the population almost doubled every decade (very roughly) between 1900 (286,000) to 1910 (466,000) to 1920 (994,000) and then again from 1920 to 1950 (1,850,000). That the decline in population (again very roughly) has lost 200,000 per decade from 1950 to 1990, then tapered to be at 917,000 as of 2007, to closely resemble what the population had been back in 1920. At least, the population slowed it's descent by only loosing roughly 50,000 per decade between 1990 and now. Could this slowing down indicate a possible rebound in the near future? I don't know, perhaps, doubtful though as it would be suggesting a break from a 50 year downward trend, that's a lot of time.
Could this graph be seen as some kind of bubble? That the population inflated to 1950 and will deflate to the levels of say, late 1800's or early 1900's? My friend Nudge, suggests this is a lot like taking a breath and then exhaling it... Could this likely happen in the next 50 years?
At this point, I can't think of a better example than Detroit, of what decline might look like for those suggesting that we'll likely loose 50% of our population in this country, 50 years from now... Can you?