## 10 Discussion
This system will be aligned with global trends towards greater data protection and individual privacy rights, potentially increasing the acceptance and trustworthiness of the system among the public and stakeholders. The key to this is to strike a balance between accurate and efficient data collection and the protection of an individual's privacy rights. Managing data provenance in a blockchain-based census system is crucial to ensuring the integrity, transparency, and trustworthiness of the data collected. Data provenance refers to the record of the origins, custody, and transformations of the data. In the context of blockchain technology, this means tracking and documenting every interaction with the data, from their initial entry into the system to their final state, including any updates or changes. Blockchain's inherent structure serves as a natural provenance tool. Its characteristics, such as an (i) immutable ledger where each block in the chain contains timestamp and transaction data, which provide an immutable record of all interactions with the data, and (ii) the traceability of the blockchain ledger allow for the complete traceability of all data transactions. This means that any changes, access, or updates to the census data can be traced back to their origin. The other way of handling this is with smart contracts. Smart contracts can be programmed to automatically record data interactions on the blockchain. For instance, when census data are updated, the smart contract can log the transaction details, including who made the change and when. A challenge may arise in that managing data with extensive provenances on a blockchain can lead to scalability issues. Nonetheless, there are a few recommendations for safeguarding and data strategies that could be combined with a blockchain census system to resolve missing persons issues more completely. The key to this is taking a multifaceted approach, combining technology, data integration, operational procedures, and governance. These recommendations are the results of the discussions carried out during our qualitative research and during the design and testing of the prototype and overall blockchain experience. * Continuous Census Data Updating: Rather than just conducting a census at fixed intervals, integrate a more continuous updating of data using civil registration systems, surveys, administrative records, and individuals' own reports. This keeps the data more dynamic and accurate. * Cross-linking of Datasets: In addition to linking census data on-chain, link them to other official government datasets like birth/death certificates, medical records, tax records, social services, etc. This provides a more holistic view of individuals and families, making it harder for people to fall through the cracks. * Privacy-preserving Record Linkage: Use statistical techniques to link individuals across datasets in a privacy-preserving way. This allows data to be integrated without compromising individuals' privacy with a public, transparent blockchain. * Offline Backups and Versioning: Maintain offline backups of census data in case the blockchain is disrupted or provides an additional level of security. Store historic versions of the data to allow for the auditing and resolution of errors. * Verification Procedures: Implement robust verification procedures to ensure that individuals are counted correctly and that the data associated with them are accurate. This could include cross-referencing other data sources, audits, and a process for individuals to report errors. * Outreach Programs: Create proactive outreach programs to identify and count marginalized groups that may be underrepresented in a census. Partner with local communities and nonprofits to improve coverage. * Governance and Security: Establish proper governance and security procedures over the census data and blockchain system to prevent unauthorized access or tampering. Add built-in auditing to monitor issues.