# How to evaluate confidence of migration events?

**URL:** <https://nextstrain.discourse.group/t/how-to-evaluate-confidence-of-migration-events/419>\
**Category:** General\
**Created:** [March 11, 2021, 4:16pm UTC](https://nextstrain.discourse.group/t/how-to-evaluate-confidence-of-migration-events/419 "2021-03-11T16:16:37Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![fhsantanna](https://avatars.discourse-cdn.com/v4/letter/f/f19dbf/32.png) [@fhsantanna](https://nextstrain.discourse.group/u/fhsantanna)\
**Post date:** [March 11, 2021, 4:16pm UTC](https://nextstrain.discourse.group/t/how-to-evaluate-confidence-of-migration-events/419/1 "2021-03-11T16:16:37Z")

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I merged the South America dataset with mine (South Brazil).  
The problem is that I have hundreads of sequences for South Brazil, so some “mugration” events do not make sense, ie some lineages appear to have arisen in South Brazil (but I am not sure that this is true, I believe it is a problem of undersampling for the rest of Brazil).

I also performed an independent phylogenetic reconstruction using only samples of certain pango lineages. Bootstrap values are very low, as expected, considering the narrow timeframe and the slow-evolving virus.

However, it makes me consider how much I can rely on the ancestral reconstruction of the nextstrain tree. How do I know if the viral migration events are in fact representing the reality?

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**Author:** ![rneher](https://yyz1.discourse-cdn.com/flex031/user_avatar/nextstrain.discourse.group/rneher/32/20_2.png) [@rneher](https://nextstrain.discourse.group/u/rneher)\
**Post date:** [March 13, 2021, 9:54am UTC](https://nextstrain.discourse.group/t/how-to-evaluate-confidence-of-migration-events/419/2 "2021-03-13T09:54:45Z")

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The migration analysis reports marginal probabilities for ancestral locations. But these probabilities assume similar sampling efforts across the tree. In absence of a carefully sampled data set, wouldn’t put much confidence in these reconstructions.

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**Author:** ![fhsantanna](https://avatars.discourse-cdn.com/v4/letter/f/f19dbf/32.png) [@fhsantanna](https://nextstrain.discourse.group/u/fhsantanna)\
**Post date:** [March 15, 2021, 4:03pm UTC](https://nextstrain.discourse.group/t/how-to-evaluate-confidence-of-migration-events/419/3 "2021-03-15T16:03:20Z")

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Thank you very much.