Mythical Man Month II

Brooke's Law doesn't include scaling effects. They're geometric. [There is another effect I can't yet name that kicks in for very large projects so they can never complete. This isn't just an asympote, but a maximum - total output reduces the bigger you make the project team without relaxing the time constraint.]

Here's the heuristic scaling law:
To double output, triple the resources.
[No evidence or research to support this.]

If you have 10 units of work to do and your staff of 6 can do it in 3 months, to produce 20 units of work in 3 months, you need 3 teams of 6 [modulo their effectiveness and project initiation time]. For 40 units, 9 teams, 80 units - 27 teams etc.
Alternatively, what the team can do in 24 months, might be possible in 3 months with 27 times more resource - or around 8 times the total cost, if it ever completes. [I don't have any ideas on the increase in unreliability of the estimates or the 'Project Risk' increase.]

Sometimes "Fast Tracking" may be necessary... But hugely expensive - and where are you going to find around 25 times as many people???

The Standish Group have been performing Primary Research (surverys) of I.T. in the USA since 1994. They've accumulated a large amount of data and 50,000 project case studies.

Their "Recipe for Success" (for I.T. projects) is simple - six people for six months.
It seems to confirm this hypothesis.

"Cheap, Fast, Good - pick any two".


From an article in "Software Magazine", Here's the list of Standish's Top Ten:

Recipe for Success: CHAOS Ten  
 
  Confidence Level Success Factors  
  Executive support  18  
  User involvement  16  
  Experienced project manager 14  
  Clear business objectives 12  
  Minimized scope   10  
  Standard software infrastructure 8  
  Firm basic requirements  6  
  Formal methodology  6  
  Reliable estimates  5  
  Other criteria   5