Federated vs. CDR Integration Approach

What is better system for integrating different Healthcare applications spread across different locations e.g. Regional or Provincial level EHR? -

1. Federated model - where data is pulled on demand
2. Central Data Repository - where all data from source systems is pooled upfront
   

This Q has troubled my mind for a long time and I am unable to find a consensus on the best approach. But after having discussed this matter extensively I felt I should post summary of all views in the blog for a wider audience.

Most Commonwealth countries are adopting the Federated model to build their HIE and EHRS. Standards such as HL7 and DICOM make it relatively simple to implement a more flexible Federated model. However how would you do Evidence based medicine 'closing the loop' and Epidemiology data analytics in Federated model? Isn't Central Data repository required for the data analytics.

Whereas Central repositories tend to be fairly brittle. Converting the source data to standard format to store in CDR is a challenge. Also, relatively small changes on the part of any of your data sources can result in all kinds of difficulties. But it is much easier to get a single, consolidated view of patient information with a CDR method.

Some people feel that we need at least some metadata or a clinical subset to be stored in a CDR fashion. That's the only way to do data analysis for outcomes measurement. A "hybrid" model is most promising i.e. Store key clinical indicators and pull other details as needed.

In summary, all depends upon what you want to achieve. Federated is the best if you want the patient data to move along with the patient in the healthcare value chain. However you will need CDR if you want to close the loop and do epidemiology analysis, evidence-based medicine or disease progression trend charting for patients.