National Review:  An Embarrassing Metric Disappears: 
Why Are Government Statistics on Taxpayer Migration Being Discontinued?:

As the din of America’s falling
headfirst over the fiscal cliff reverberates across the nation, the
Obama administration is quietly killing a key economic metric that tells
how, and how many, people are voting with their feet. Since 1991 the
IRS has been compiling statistics on filers’
addresses, which the agency’s Statistics of Income division uses to show
who is moving into and out of every county and state in the nation. As
you’d expect, the IRS also knows the aggregate income levels of those
who move. So the movements of the most fundamental productive components
of the economy — taxpayers — can be analyzed by journalists and economists, or could until now.

The IRS and the U.S. Census Bureau (which provides technical support
in reporting tax migration data) have not made an official announcement
as to why the program is being discontinued. So we are left to speculate
why such vital economic statistics suddenly got canceled.

Some would be glad if the IRS data simply went away. Blue states with
high state and local tax burdens have come out looking bad in recent
years. California [, Maryland] and New York have been embarrassed publicly, as a
steady exodus is underway from both. …

While it remains to be seen what the official position of the IRS is,
unofficially it is suggesting that the problem lies in coordinating
with the Census Bureau. It is asking for comments on how people use the
data and how important it is, presumably so that higher-ups at the
agencies can reverse their decision if necessary.

The very idea of people voting with their feet is uncomfortable to
some politicians. Fortunately, others realize the damage that a
declining tax base causes and prefer transparency over attempting to
delete statistics that reveal the problem.