# How VDS handles missing data?

**URL:** <https://discuss.hail.is/t/how-vds-handles-missing-data/4149>\
**Category:** Hail Query & hailctl\
**Created:** [May 27, 2025, 4:42pm UTC](https://discuss.hail.is/t/how-vds-handles-missing-data/4149 "2025-05-27T16:42:41Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![zengchenjie](https://yyz2.discourse-cdn.com/flex036/user_avatar/discuss.hail.is/zengchenjie/32/1298_2.png) [@zengchenjie](https://discuss.hail.is/u/zengchenjie)\
**Post date:** [May 27, 2025, 4:42pm UTC](https://discuss.hail.is/t/how-vds-handles-missing-data/4149/1 "2025-05-27T16:42:41Z")

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I wonder if missing/unstored calls are assumed to be homozygous reference unless otherwise specified in VDS format. Thanks.

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**Author:** ![chrisvittal](https://yyz2.discourse-cdn.com/flex036/user_avatar/discuss.hail.is/chrisvittal/32/327_2.png) [@chrisvittal](https://discuss.hail.is/u/chrisvittal)\
**Post date:** [May 27, 2025, 4:49pm UTC](https://discuss.hail.is/t/how-vds-handles-missing-data/4149/2 "2025-05-27T16:49:54Z")

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No?

Like any genotype, the data can be present or missing. The distinction with VDS is that reference calls are run length encoded over regions to save on size.

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**Author:** ![zengchenjie](https://yyz2.discourse-cdn.com/flex036/user_avatar/discuss.hail.is/zengchenjie/32/1298_2.png) [@zengchenjie](https://discuss.hail.is/u/zengchenjie)\
**Post date:** [May 27, 2025, 6:57pm UTC](https://discuss.hail.is/t/how-vds-handles-missing-data/4149/3 "2025-05-27T18:57:28Z")

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Thanks! This is helpful!