# BLAST consensus question

**URL:** https://forum.qiime2.org/t/blast-consensus-question/24200
**Category:** User Support
**Tags:** taxonomy, feature-classifier, dada2
**Created:** [September 19, 2022, 2:49pm UTC](https://forum.qiime2.org/t/blast-consensus-question/24200 "2022-09-19T14:49:07Z")
**Posts on this page:** 1
**Showing post:** 2

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### Author: ![SoilRotifer](https://forum.qiime2.org/user_avatar/forum.qiime2.org/soilrotifer/32/21071_2.png) [@SoilRotifer](https://forum.qiime2.org/u/SoilRotifer)
#### Post date: [September 19, 2022, 2:59pm UTC](https://forum.qiime2.org/t/blast-consensus-question/24200/2 "2022-09-19T14:59:37Z")

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Hi @Newt,

I suspect, that part of the reason why `classify-consensus-blast` is ultimately choosing _Dendrodrilus rubidus_, has to do with the `--p-min-consensus` setting. If you read the help documentation by running:

```auto
qiime feature-classifier classify-consensus-blast --help

```

You'll see that the help text for `--p-min-consensus` says:

```auto
--p-min-consensus NUMBER Range(0.5, 1.0, inclusive_start=False,
    inclusive_end=True) Minimum fraction of assignments must match top hit
    to be accepted as consensus assignment. [default: 0.51]

```

This setting, as well as what sequence data is ultimately included within your curated reference database, can alter the taxonomy consensus assignment.

> [@Newt](#):
>
> I'm a little concerned about using a species level classification if NCBI blast is identifying multiple species with 100% identity. I'm wondering if I should move classification down to a different level if the sequence belongs to multiple species.

This is quite common with short-read amplicon data. Which is why there are a variety of consensus approaches (vsearch & BLAST), and other taxonomy assignment tools (scikit-learn, RDP,...) out there.

Also, I recommend trying this new [RESCRIPt approach](https://forum.qiime2.org/t/using-rescripts-extract-seq-segments-to-extract-reference-sequences-without-pcr-primer-pairs/23618) for generating a reference database from GenBank data.

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