NA in various columns in "research"

[hughjonesd]

Here are some columns of research along with the number of NA values. Note, I don't look at columns that aren't imported as public data.

• I think "status" and "research_url" probably should not be NA.
• In general, if a column can be NA, we should document why that might happen and/or what it means.

         label_paper_title                     status               research_url 
                         0                         37                         20 
                       doi             main_cause_cat        secondary_cause_cat 
                       171                          8                        132 
        publication_status working_paper_release_date             topic_subfield 
                        80                        163                        103 
               source_main 
                        74