text: SELECT
          ev_cat,
          COUNT(distinct(doi)) AS number_of_articles 
      FROM(
          SELECT
                  doi,
                  STRING_AGG(DISTINCT(evidence), "&" ORDER BY evidence) AS ev_cat
              FROM
                  `oadoi_full.feb_19_mongo_export_2013_Feb2019_full_all_genres`,
                  UNNEST(oa_locations)
              WHERE
                  genre = 'journal-article'
                  AND year < 2019
              GROUP BY
                  doi
      )
      GROUP BY
          ev_cat