ISPOR have recently published 
guidelines on the validation of ePRO systems.  They highlight and describe 8 essential components of the validation process.  These being:
- System requirements
- System design
- Coding/tailoring/software development
- Testing by system provider
- Traceability
- UAT
- Installation/configuration management
- Decommissioning plan
The guidelines do not, however, get into the tricky business of whether the e-version of PROMs get the same results as the paper version, how best to get patients to complete, respond, collect folow-up data etc., or whether there are any specific validation issues relating to ePROs.
HEDS are developing a programme of research that covers these topics.  Contact Professor 
John Brazier or 
Dr Georgina Jones for further details.