[PopeDotNinja]

In my experience, providing effective estimates with actual data requires:

- know enough about what you are doing to estimate at all

- screening for clients who will make it possible to work effectively, and knowing how to do that

-setting realistic expectations about what can actually be accomplished

- the client has the resources to pay for the project, including multiple iterations of dealing with the unexpected

- you the resources to make efficient use of the clients resources

- you don't promise to deliver something that you quoted at a higher price when the client talks you down to a lower price