Uganda   82 studies
Ukraine   377 studies
United Arab Emirates   18 studies
United Kingdom   3323 studies
United States   37270 studies
    United States, Alabama   3440 studies
    United States, Alaska   224 studies
    United States, Arizona   3452 studies
    United States, Arkansas   1851 studies
    United States, California   10465 studies
    United States, Colorado   3568 studies
    United States, Connecticut   2649 studies
    United States, Delaware   880 studies
    United States, District of Columbia   2368 studies
    United States, Florida   6875 studies
    United States, Georgia   4380 studies
    United States, Hawaii   863 studies
    United States, Idaho   806 studies
    United States, Illinois   6168 studies
    United States, Indiana   3642 studies
    United States, Iowa   2030 studies
    United States, Kansas   2259 studies
    United States, Kentucky   2403 studies
    United States, Louisiana   2742 studies
    United States, Maine   769 studies
    United States, Maryland   7279 studies
    United States, Massachusetts   6001 studies
    United States, Michigan   4652 studies
    United States, Minnesota   3929 studies
    United States, Mississippi   1188 studies
    United States, Missouri   4498 studies
    United States, Montana   971 studies
    United States, Nebraska   2110 studies
    United States, Nevada   1521 studies
    United States, New Hampshire   916 studies
    United States, New Jersey   3998 studies
    United States, New Mexico   1287 studies
    United States, New York   9177 studies
    United States, North Carolina   5936 studies
    United States, North Dakota   899 studies
    United States, Ohio   6474 studies
    United States, Oklahoma   2317 studies
    United States, Oregon   2897 studies
    United States, Pennsylvania   7188 studies
    United States, Rhode Island   1463 studies
    United States, South Carolina   3186 studies
    United States, South Dakota   752 studies
    United States, Tennessee   4166 studies
    United States, Texas   8874 studies
    United States, Utah   2066 studies
    United States, Vermont   947 studies
    United States, Virginia   3597 studies
    United States, Washington   4243 studies
    United States, West Virginia   841 studies
    United States, Wisconsin   2931 studies
    United States, Wyoming   218 studies
Uruguay   26 studies
Uzbekistan   1 study