> For the complete documentation index, see [llms.txt](https://docs.finngen.fi/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.finngen.fi/finngen-data-specifics/finnish-health-registers-and-medical-coding/data-masking-blurring-of-visit-dates.md).

# Data Masking/Blurring of Visit Dates

All FinnGen individual-level data is pseudo-anonymised: Personal Identity codes (PICs) are replaced by FinnGen IDs, and **only pseudo-anonymised individual-level data can be found in Sandbox.**

### < 5 cases rules

In **DF1-DF7** all register codes with less that five cases within detailed longitudinal data, and all endpoints with less than 5 cases in endpoint and longitudinal endpoint data **have been removed** from the data.

**DF8v3 onwards** all register codes in detailed longitudinal data and all endpoints in endpoint and endpoint longitudinal data, also those with less than 5 cases, **are included** in the data released to the Sandbox.

### Randomized event days

In order to protect individual-level data, exact event days cannot be released with phenotype data. Exact event dates are randomized to an approximated event day (`APPROX_EVENT_DAY`) by adding **+/- 1-15 days** (offset) to the exact event day.

The number added to the exact event day is consistent within individual (*individual-specific*), meaning that the same number (offset) is added to all events of the individual.

* **Until DF10, offset** **is not consistent across registers**. The `APPROX_DAY` is usually calculated separately in each register (eg. [reproductive history data](/finngen-data-specifics/red-library-data-individual-level-data/what-phenotype-files-are-available-in-sandbox-1/other-registers.md) vs. [service sector data](/finngen-data-specifics/red-library-data-individual-level-data/what-phenotype-files-are-available-in-sandbox-1/other-registers.md)). However in the [detailed longitudinal data](/finngen-data-specifics/red-library-data-individual-level-data/what-phenotype-files-are-available-in-sandbox-1/detailed-longitudinal-data.md) the same individual-specific offset is used for particular individual in all registers included in the data.
* **From DF11 forward offset is consistent across registers**. Same offset per person (consistent for all event of 1 person) is used for all FinnGen register files.