```eval_rst
.. _datthcomp:
```
# How to do a data theory comparison

This tutorial explains how to compare the data and theory for a given data set or list of data sets.

You need to provide:

1. A PDF which includes your data set;
2. A valid theory ID;
3. A choice of cuts policy;
4. A list of data sets to do the comparison for.

Below is an example runcard for a data theory comparison for BCDMSP, `runcard.yaml`:
```yaml
meta:
    title: BCDMSP data/theory comparison
    keywords: [example]
    author: Rosalyn Pearson

pdfs: 
    - id: NNPDF31_nnlo_as_0118
      label: NNPDF31_nnlo_as_0118

theoryid: 53

use_cuts: false

dataset_inputs:
      - { dataset: BCDMSP}

template: dthcomparison.md

actions_:
  - report(main=true)
```

The corresponding template, `dthcomparison.md`, looks like this:
```yaml
%BCDMSP (theory ID 52)

{@ dataset_inputs plot_fancy @}
{@ dataset_inputs::pdfs plot_fancy(normalize_to=data)@}
{@ dataset_inputs::pdfs plot_chi2dist @}
{@ dataset_inputs::pdfs group_result_table @}
```

1. `plot_fancy` produces data-theory comparison plots for the data. This is called twice to produce both normalised and unnormalised sets of plots.
2. `plot_chi2dist` gives the chi2 distribution between the theory and data.
3. `group_result_table` gives the numerical values which appear in the plots.

Running `validphys runcard.yaml` should produce a `validphys` report of the data-theory comparison like the one [here](https://vp.nnpdf.science/ErmVZEPGT42GCfreWwzalg==/) - see the
[vp-guide](https://data.nnpdf.science/validphys-docs/guide.html#development-installs).