# Dada2 filtering out \>80% of reads as chimeras!

**URL:** https://forum.qiime2.org/t/dada2-filtering-out-80-of-reads-as-chimeras/7866
**Category:** Technical Support
**Created:** [January 17, 2019, 1:25pm UTC](https://forum.qiime2.org/t/dada2-filtering-out-80-of-reads-as-chimeras/7866 "2019-01-17T13:25:42Z")
**Posts on this page:** 1
**Showing post:** 24

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### Author: ![YaochunYu](https://forum.qiime2.org/user_avatar/forum.qiime2.org/yaochunyu/32/4495_2.png) [@YaochunYu](https://forum.qiime2.org/u/YaochunYu)
#### Post date: [April 30, 2019, 10:20pm UTC](https://forum.qiime2.org/t/dada2-filtering-out-80-of-reads-as-chimeras/7866/24 "2019-04-30T22:20:24Z")

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Hi Sam,

in dada2, it is recommend to use a value greater than or equal to 1 for the commoan "--p-min-fold-parent-over-abundance FLOAT". Thus can I ask the reason why you used a 0.75 for you data analysis?

I am not 100% understand the command, but please check this out: [large percentage of merged reads flagged as chimeric, but not due to primers · Issue #602 · benjjneb/dada2 · GitHub](https://github.com/benjjneb/dada2/issues/602)  
Ben @benjjneb mentioned that a higher value (e.g. 4/8) could prevent the FP chimera.

And also please check my post: [The meaning of DADA2 command "--p-min-fold-parent-over-abundance FLOAT"](https://forum.qiime2.org/t/the-meaning-of-dada2-command-p-min-fold-parent-over-abundance-float/9454)

Recently I run into the similar issue, the sequence after merging is still good, bot after the chimera check, it lost ~80%. I tried to trim more sequences off and use the "--p-min-fold-parent-over-abundance 8" ~80% sequences are retained. I am now doing the taxonomy assign. I will keep updating.

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