A lot of big companies seem to hire two different kinds of software
engineers - ones who actually design and write the programs, and ones
who are involved in testing and quality assurance. How does the demand
for those two different kinds of programmers compare? Does one group
earn higher wages than the other?

Hello Gremlin,

Depending on the company, the ratio of software developers to quality
assurance personnel can be in the range of 20:1 or more. Now, you
asked about "testing and QA" - if you look at the software development
process beginning at unit test (as done in a cleanroom organization),
the ratio may be significantly reduced to perhaps 3:1, but even in
that case the software developers will greatly outnumber the quality
assurance personnel.

To give you an idea of the relative effort, see the COCOMO II site at
  http://sunset.usc.edu/research/COCOMOII/
which has a number of papers and software for this cost model. Many of
the papers refer to the total effort, but a few include relative
effort of phases. If you download the software, enter a small project
into the tool and it will show the relative effort (for development,
testing, ...).

In a similar manner, the software developers will have slightly higher
wages than the quality assurance staff. In most companies, they are
both treated as "engineers" and will have the same salary ranges.
However, there are a number of wage / salary studies which show the
development groups with 5-15% higher salary than the QA groups. For
example
  http://www.perssyst.com/whatsnew_ITsalaries.htm
shows development managers earning $104,000 while QA managers earn
$94,000. Similarly
  http://www.compinsight.com/pdfs/ITJobsNavigate_2001Report.pdf
shows a similar difference.

To find additional information, search using phrases such as
  salary software development quality assurance
  wages software development quality assurance
  software cost model
  software effort distribution by phase

  --Maniac