# Explanation of the confidence values

**URL:** <https://community.purpleair.com/t/explanation-of-the-confidence-values/1766>\
**Category:** Data\
**Created:** [August 28, 2022, 5:15pm UTC](https://community.purpleair.com/t/explanation-of-the-confidence-values/1766 "2022-08-28T17:15:48Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![posburn](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/posburn/32/1054_2.png) [@posburn](https://community.purpleair.com/u/posburn)\
**Post date:** [August 28, 2022, 5:15pm UTC](https://community.purpleair.com/t/explanation-of-the-confidence-values/1766/1 "2022-08-28T17:15:48Z")

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I see the confidence properties listed in the API documentation but there is no explanation of them. Specifically, what is the difference between confidence, confidence\_auto, and confidence\_manual?

When calculating AQI I’m trying to decide when to average the pm cf values for A and B, and when to just use either A or B based on the confidence of each sensor. Is that possible? If so, what confidence threshold is recommended?

Thanks,

Paul

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**Author:** ![dwhitemv](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/dwhitemv/32/1508_2.png) [@dwhitemv](https://community.purpleair.com/u/dwhitemv)\
**Post date:** [August 30, 2022, 4:17pm UTC](https://community.purpleair.com/t/explanation-of-the-confidence-values/1766/2 "2022-08-30T16:17:03Z")

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As an alternative, you can use the EPA’s data removal criteria for their NowCast calculations of PA sensors:

Points removed if 24-hr averaged A & B PM2.5 differ by

- ≥ ± 5 μg\*m-3 AND
- ≥ ± 2\*sd(% error)
  - 56% for 24-hr data
  - 70% for 1-hr data

Source: [PurpleAir PM2.5 U.S. Correction and Performance During Smoke Events 4/2020 | Science Inventory | US EPA](https://cfpub.epa.gov/si/si_public_record_report.cfm?Lab=CEMM&dirEntryId=349513)

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**Author:** ![JerryN](https://avatars.discourse-cdn.com/v4/letter/j/ecccb3/32.png) [@JerryN](https://community.purpleair.com/u/JerryN)\
**Post date:** [March 5, 2023, 5:45pm UTC](https://community.purpleair.com/t/explanation-of-the-confidence-values/1766/3 "2023-03-05T17:45:37Z")

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I’d like to know how PA defines these variables. Is there a data dictionary somewhere?

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**Author:** ![Rhkirby](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/rhkirby/32/2444_2.png) [@Rhkirby](https://community.purpleair.com/u/Rhkirby)\
**Post date:** [January 10, 2024, 5:42pm UTC](https://community.purpleair.com/t/explanation-of-the-confidence-values/1766/4 "2024-01-10T17:42:37Z")

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> [@JerryN](#):
>
> there a data dictionary somewhere?

Hi, I would also like to know this information. I’m seeking specifics on defining confidence and what 100% confidence means.

Thanks!