I have discovered some numbers that didn't add up in my previous calculations while adding the numbers for 2012-2015, and so redid the additions (this time in Excel, not by hand). The outcome is more encouraging: 32% female authors overall (not the wrong 25%). Among single authors the proportion of women is 29% (not 20%), raising to 36% (not 30%) in co-authored articles.
5 co-authored articles were written solely by women (13 authors) vs. 21 articles that were co-authored solely by men (47 authors). This gives us 5/26 =19% of female articles for articles co-authored by authors of the same gender (13/60 = 22% of females in that group of authors).
The proportion of women (not "female articles") for single-authored and co-authored articles is 29% and 22%, respectively.
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Compare these ratios to overall results for Women in Linguistics
| issue | single author | co-authored | publications overall |
| 1998, 1.1 | 0/2 | 1/2+0/2 | 1/6 |
| 1998, 1.2 | 1/3 | 0/2 | 1/5 |
| 1998, 1.3 | 1/2 | 1/2 | 2/4 |
| 1999, 2.1 | 1/2 | 0/2 | 1/4 |
| 1999, 2.2 | 2/2 | 2/2+1/2 | 5/6 |
| 1999, 2.3 | 0/3 | 0/3 | |
| 2000, 3.1 | 0/1 | 3/4 | 3/5 |
| 2000, 3.2 | 0/3 | 0/2 | 0/5 |
| 2000, 3.3 | 0/2 | 1/4 | 1/6 |
| 2001, 4.1 | 0/2 | 1/2 | 1/4 |
| 2001, 4.2 | 0/3 | 0/3 | |
| 2001, 4.3 | 0/2 | 1/4 | 1/6 |
| 2002, 5.1 | 0/1 | 2/3+0/2 | 2/6 |
| 2002, 5.2 | 2/2 | 2/2 | |
| 2002, 5.3 | 2/3 | 2/3 | |
| 2003, 6.1 | 2/2 | 1/2+4/4 | 7/8 |
| 2003, 6.2 | 0/2 | 0/2 | 0/4 |
| 2003, 6.3 | 0/3 | 0/3 | |
| 2004, 7.1 | 0/1 | 1/2+1/2 | 2/5 |
| 2004, 7.2 | 0/2 | 1/3 | 1/5 |
| 2004, 7.3 | 1/1 | 1/2 | 2/3 |
| 2005, 8.1 | 0/3+1/2+0/2+1/2 | 2/9 | |
| 2005, 8.2 | 0/1 | 1/2 | 1/3 |
| 2005, 8.3 | 1/2 | 1/3 | 2/5 |
| 2006, 9.1 | 0/2 | 2/2 | 2/4 |
| 2006, 9.2 | 0/2 | 0/2+0/2+0/2+1/2 | 1/8 |
| 2006, 9.3 | 1/2 | 1/2 | 2/4 |
| 2007, 10.1 | 0/2 | 0/2 | 0/4 |
| 2007, 10.2 | 0/2 | 0/2 | 0/4 |
| 2007, 10.3 | 1/2 | 1/2 | |
| 2008, 11.1 | 2/3 | 2/3 | |
| 2008, 11.2 | 0/1 | 1/2+1/3 +1/2 | 3/8 |
| 2008, 11.3 | 1/4 | 1/4 | |
| 2009, 12.1 | 1/2 | 1/2 | 2/4 |
| 2009, 12.2 | 0/1 | 1/3+2/2 | 3/6 |
| 2009, 12.3 | 1/2 | 3/3 | 4/5 |
| 2009, 12.4 | 1/2 | 1/2 | |
| 2010, 13.1 | 0/2 | 1/2 | 1/4 |
| 2010, 13.2 | 0/2 | 0/2 | 0/4 |
| 2010, 13.3 | 1/1 | 1/2+1/2 | 3/5 |
| 2010, 13.4 | 0/1 | 1/2+0/2 | 1/5 |
| 2011, 14.1 | 0/4 | 0/4 | |
| 2011, 14.2 | 1/2 | 1/2+0/4 | 2/8 |
| 2011, 14.3 | 3/3 | 3/3 | |
| 2011, 14.4 | 1/2 | 1/4 | 2/6 |
| 2012, 15.1 | 0/1 | 0/2+1/2 | 1/5 |
| Corrected subtotals: |
27/92 = 29% | 47/123 = 38% | 74/215 = 34% |
| 2012, 15.2 | 1/2 | 0/2 | 1/4 |
| 2012, 15.3 | 1/3 | 1/3 | |
| 2012, 15.4 | 1?/1 | 0/3 | 1?/4 |
| 2013, 16.1 | 0/3 | 0/3 | |
| 2013, 16.2 | 0/2 | 0/2 | 0/4 |
| 2013, 16.3 | 1/2 | 1/2 | 2/4 |
| 2013, 16.4 | 2/3 | 2/3 | |
| 2014, 17.1 | 0/3 | 0/3 | |
| 2014, 17.2 | 2/3 | 2/3 | |
| 2014, 17.3 | 1/2 | 1/2 | 2/4 |
| 2014, 17.4 | 0/3 | 0/3 | |
| 2015, 18.1 | 0/2 | 0/3 | 0/5 |
| 2015, 18.2 | 0/3 | 0/3 | |
| 2015, 18.3 | |||
| 2015, 18.4 | |||
| Total: | 36?/124 = 29% | 49/137 = 36% | 85?/261 = 32% |