An economic study conducted by a left-of-center research and economic policy group has found that, while the United States has added about 4 million jobs since the end of the recession, they have not been the same sort of jobs that were lost.

That offers one empirical reason why, despite the fact the economy is growing, many people say they think it is still in recession.

The report, published by the National Employment Law Project, says the difference is that rising employment numbers still have replaced only about 60 percent of the 7 million jobs lost over the two-year period from the first quarter of 2008 to the low point for the work force, which was in the first quarter of 2010.

But even more significantly, the study shows, the new jobs have, on average, paid lower wages than the ones that were lost. So, while mid-level jobs (defined as those making roughly $14 to $21 per hour) went down by 4 million positions during the recession, they have accounted for only less than 1 million of new hires.

Low-level jobs (roughly $7.50 to $14 per hour) declined only by 1.3 million positions, but accounted for 2 million new jobs. (Higher-level spots, at $21 to $55 per hour, lost 1.1 million jobs and gained back about 750,000, the study shows. All figures are rounded.)

Thus, many of the new jobs were either entry-level positions taken by people new to the work force, or were filled by people who had lost higher-paying jobs and could find only ones that offered less compensation.

Given those conditions, it is no wonder economic optimism remains low even in a recovery, the group said.

Within the groups, low-level jobs include retail sales and food preparation; mid-level jobs are found in the construction, manufacturing and information fields, and high-level positions include medicine, law and many government jobs, including education.

The study says a major part of the higher-level job losses involve work force cuts in the public sector, mostly in state and local governments. The group recommends that states get more grants for public jobs and funding for infrastructure projects to employ more construction workers.

That funding, however, probably depends on the outcome on Nov. 6.