Canada   5840 studies
    Canada, Alberta   1673 studies
    Canada, British Columbia   1670 studies
    Canada, Manitoba   786 studies
    Canada, New Brunswick   366 studies
    Canada, Newfoundland and Labrador   435 studies
    Canada, Nova Scotia   903 studies
    Canada, Ontario   3830 studies
    Canada, Prince Edward Island   107 studies
    Canada, Quebec   2303 studies
    Canada, Saskatchewan   647 studies
Mexico   951 studies
United States   39810 studies
    United States, Alabama   3629 studies
    United States, Alaska   239 studies
    United States, Arizona   3662 studies
    United States, Arkansas   1944 studies
    United States, California   11088 studies
    United States, Colorado   3760 studies
    United States, Connecticut   2816 studies
    United States, Delaware   910 studies
    United States, District of Columbia   2482 studies
    United States, Florida   7302 studies
    United States, Georgia   4585 studies
    United States, Hawaii   894 studies
    United States, Idaho   857 studies
    United States, Illinois   6515 studies
    United States, Indiana   3828 studies
    United States, Iowa   2108 studies
    United States, Kansas   2398 studies
    United States, Kentucky   2561 studies
    United States, Louisiana   2857 studies
    United States, Maine   815 studies
    United States, Maryland   7576 studies
    United States, Massachusetts   6320 studies
    United States, Michigan   4910 studies
    United States, Minnesota   4119 studies
    United States, Mississippi   1243 studies
    United States, Missouri   4776 studies
    United States, Montana   1007 studies
    United States, Nebraska   2221 studies
    United States, Nevada   1590 studies
    United States, New Hampshire   967 studies
    United States, New Jersey   4200 studies
    United States, New Mexico   1353 studies
    United States, New York   9648 studies
    United States, North Carolina   6251 studies
    United States, North Dakota   970 studies
    United States, Ohio   6847 studies
    United States, Oklahoma   2436 studies
    United States, Oregon   3040 studies
    United States, Pennsylvania   7549 studies
    United States, Rhode Island   1544 studies
    United States, South Carolina   3312 studies
    United States, South Dakota   776 studies
    United States, Tennessee   4433 studies
    United States, Texas   9439 studies
    United States, Utah   2192 studies
    United States, Vermont   991 studies
    United States, Virginia   3797 studies
    United States, Washington   4463 studies
    United States, West Virginia   888 studies
    United States, Wisconsin   3071 studies
    United States, Wyoming   128 studies