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Description

HIK is a universal identifier key used to track individuals across historical censuses.

HIKs are the product of a complex linking process developed by the Multigenerational Longitudinal Panel (MLP) project. The MLP project and a description of the linking process are described at the Multigenerational Longitudinal Panel home page.

Individuals can be linked across time spans as long as 80 years. The linking process matches records across 10, 20, and 30 year census pairs, and these links are then chained together into a single HIK. Because the constituent links include non-adjacent censuses, the chain of links within a HIK can skip over ten and twenty years gaps in which we were unable to identify an individual.

We expect to continue improving the linking algorithm in the coming years, applying new data and techniques. If the relationship between any of the person identifiers (HISTIDs) and a HIK change, the old HIK will be permanently discarded and a new HIK will be generated. Old (obsolete) HIKs will be archived and made available for download. The variable VERSIONHIK indicates the revision number of the census data and the MLP linking database; users working with older versions of the data should be mindful that changes to HIKs can occur with the release of revised data. Please refer to the comparability tab for a discussion of the differences between versions of the MLP linking data.