 href="../articles/variables_sheet.html">variables.csv sheet</a>
    </li>
    <li>
      <a href="../articles/variable_details.html">variable_details.csv sheet</a>
    </li>
    <li>
      <a href="../articles/derived_variables.html">Derived variables</a>
    </li>
    <li>
      <a href="../articles/how_to_add_variables.html">How to add variables</a>
    </li>
    <li>
      <a href="../articles/tagged_na_usage.html">How to use tagged_na</a>
    </li>
    <li>
      <a href="../articles/duplicate_datasets