Science and Engineering Indicators (SEI) is prepared by the National Science Foundation’s Division of Science Resources Statistics (SRS) under the guidance of the National Science Board. The information reported in SEI is intended to contribute to an understanding of the current environment and to inform the development of future policies.

This tool includes seven core chapters and an appendix providing detailed data tables keyed to each chapter.
The chapter 3 “Science and Engineering Labor Force” and especially “Labor Market Conditions for Recent S&E Graduates” sub-chapter, are particularly interesting for us.
This section looks at a number of standard labor market indicators for recent S&E degree recipients at all levels, and examines a number of other indicators that may apply only to recent S&E doctorate recipients.
For example, datas show that although a doctorate degree opens career opportunities both in terms of salary and type of employment, that only becomes true after several years of work. The increase in likelihood and length of postdoc positions is a good illustration.
Furthermore, unemployment rate for recent S&E doctoral degree recipients (1-3 years after receiving doctorate) fell from 2.3 % in 2003 to 1.3 % in 2006.
In 2006 for all fields of degree, the median annual salary for this population (1-5 years after degrees) was $52,000. By type of employment, salaries range from $40,000 for postdoc positions to $80,000 for those employed by private for-profit business.

SEI is released in printed and electronic formats and is posted on line at http://www.nsf.gov/statistics/indicators/ in html format and pdf, with text and appendix tables, and source data for each figure available in spreadsheet (MS Excel) format. Selected figures are also available in Powerpoint and Jpeg formats.

In conclusion, you can easily and pleasantly find among the significant volume of available datas, the information that you are searching for.

Science and Engineering Indicators 2008 : The American bible