Test Effort Estimation

For a long time, I wonder about the effort estimation on Software testing. Recently I read a piece of information on this,

How do managers estimate the effort needed for software testing? There may be many in house and practical gut-feeling methods, but scientifically, the following methods are used,

- 'Percentage-of-Development' approach
- Implicit Risk-Context approach
- Metrics based approach
- Test work breakdown approach
- Iterative approach


The practical 'gut-feeling' approach may or may not indirectly follow the abovesaid approaches. None of the methods are 'recommended', as the best.