I work in a colorful testing team.  By colorful, I mean they are from various backgrounds in terms of undergraduate education.  Of course, at the beginning of work, they got training around software testing.  Most of testers have not developer background (let’s say NonTech and Tech), only a few of them including me. 

At first I thought, developers would be great testers.  Then throughout the work experience I have seen that developers are not the good ones.  In terms of bug count, developers were definitely bad ones.  So I thought, why would staff testing team with developers.  NonTechs especially were good at catching appearance issue, invalid data issue.  Also, some are more expressive with bug reports and good at writing definitive steps.  So, testing team should be staffed with NonTechs only. 

But then I have realized something.  For once, we have tested an application.  We have found great many bugs with that small application.  Of course, application developers were not so happy with this.  They were complaining about finding unnecessary bugs that were not related to normal operation of the application.

In contrary with NonTechs, Techs are not expressive enough mostly (of course there are good ones.).  Also, assuming that developers would understand, Techs tend to ignore some basic steps to reproduce bugs.  Techs also tend to test according to normal operation.

So, what is the right ratio of Tech and NonTechs?