The 11-12% refers to wages and salaries.
The 6.8% to 7.4% refers to benefit compensation.
The article was not as clear as it could be,
From the NIRS study:
The analysis finds that:
*Public and private workforces differ in important
ways. For instance, jobs in the public sector require
much more education on average than those in
the private sector. Employees in state and local
sectors are twice as likely as their private sector
counterparts to have a college or advanced degree.
*Wages and salaries of state and local employees are
lower than those for private sector workers with
comparable earnings determinants (e.g., education).
State employees typically earn 11 percent less; local
workers earn 12 percent less.
*Over the last 20 years, the earnings for state and
local employees have generally declined relative to
comparable private sector employees.
*The pattern of declining relative compensation
remains true in most of the large states we
examined, although some state-level variation
exists.
*Benefits (e.g., pensions) comprise a greater share of
employee compensation in the public sector.
*State and local employees have lower total
compensation than their private sector counterparts.
On average, total compensation is 6.8 percent lower
for state employees and 7.4 percent lower for local
workers, compared with comparable private sector
employees.
http://www.nirsonline.org/storage/nirs/documents/final_out_of_balance_report_april_2010.pdf