Hi,

You can find a detailed classification of existing methods and tools for software estimation on the following web links:

http://www.tfzr.uns.ac.rs/emc/emc2011/Files/F%2003.pdf

http://www.computing.dcu.ie/~renaat/ca421/LWu1.html

I would suggest you to go consult the work of Magne Jørgensen (https://www.simula.no/people/magnej). Hope this will help.

You can have a look at this (https://www.researchgate.net/publication/313249782_EffortEst-_An_Enhanced_Software_Effort_Estimation_by_Analogy_Method) which is on effort estimation. I hope it is useful.

Article EffortEst- An Enhanced Software Effort Estimation by Analogy Method

I'll follow Scott's example by recommending some of my own practical experience:

Conference Paper Estimating Application Management

If you need good data to test your models on, you should contact ISBSG for access to their database. They have a lot of maintenance data available.

International Software Benchmarking Standards Group

http://www.isbsg.org