# Combining Datasets with 2 sets of Primers

**URL:** https://forum.qiime2.org/t/combining-datasets-with-2-sets-of-primers/3073
**Category:** User Support
**Tags:** dada2, merge, primers
**Created:** [February 16, 2018, 6:21pm UTC](https://forum.qiime2.org/t/combining-datasets-with-2-sets-of-primers/3073 "2018-02-16T18:21:48Z")
**Posts on this page:** 1
**Showing post:** 10

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### Author: ![colinbrislawn](https://forum.qiime2.org/user_avatar/forum.qiime2.org/colinbrislawn/32/6221_2.png) [@colinbrislawn](https://forum.qiime2.org/u/colinbrislawn)
#### Post date: [February 17, 2018, 11:47pm UTC](https://forum.qiime2.org/t/combining-datasets-with-2-sets-of-primers/3073/10 "2018-02-17T23:47:39Z")

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Good afternoon,

> [@jbethany](#):
>
> variations were causing identical sequences to be labeled separately

> [@Nicholas\_Bokulich](#):
>
> but even a 1 nt difference is enough to cause two otherwise identical sequences (with 1 nt difference) to become separate features

This is true of the dada2 denoising algorithm; it's very sensitive to small biological differences, and also to small technical variation. The older OTU picking methods are much less sensitive to this; default of (97% similar == 3% diff) \* 300 bp = 9 bp diff can be in a single OTU.

High precision methods may not be a good fit for a messy data set. Greedy heuristic clustering lacks accuracy and precision, but it's flexibility and tolerance make it a reasonable solution for funky data sets. 🙈

Colin

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