The Independent number surprised me a little.
Karin,
The number is not reliable. Here's why:
The 2006 poll had three options for political identity:
A. Republican
B. Democrat
C. Independent (not A and not B)
The 2013 poll had three options:
D. Republican
E. Democrat
F. Independent (not D and not E)
C is made up of people who did not identify themselves as members of the Republican or Democrat Parties
in 2006; F is made up of people who did not identify themselves as members of either party
in 2013. C and F can include people who are hard left, hard right, moderate, and apolitical (everything from libertarians to anarchists to communists to "no opinion"). The people who are lumped into C and F are vastly different from each other, so we have no way to identify
characteristics of C or F aside from "not Republican or Democrat".
Added to that is the TEA Party, which did not exist in 2006. It is reasonable to think that people who call themselves
TEA Party members in 2013 called themselves
Republicans in 2006.
C =/= F, so we can't compare them to reach a conclusion which can be generalized.