Thanks to gavinballard for the CSV link.
If you want to see different breakdowns, just download the workbook/software and play with it yourself.
Where do developers disappear after 8 years? And then pop back up after 12.
The answer could be that the bubble burst.
The half-life of a software engineer is about 5-6 years. To understand this, keep in mind that most of "software" isn't working on cutting-edge problems using high-productivity languages. It's Java/C++ legacy maintenance and crufty business logic. A substantial fraction of law and business school students are programmers who landed in enterprise Java jobs and bored out after a few years.
I think they are useful when the decreased value of other metrics than our target metric is more appealing than the increased value of our target metric itself.Example: share of profit.