Uganda   83 studies
Ukraine   382 studies
United Arab Emirates   18 studies
United Kingdom   3371 studies
United States   37650 studies
    United States, Alabama   3466 studies
    United States, Alaska   228 studies
    United States, Arizona   3483 studies
    United States, Arkansas   1867 studies
    United States, California   10545 studies
    United States, Colorado   3598 studies
    United States, Connecticut   2665 studies
    United States, Delaware   888 studies
    United States, District of Columbia   2381 studies
    United States, Florida   6923 studies
    United States, Georgia   4425 studies
    United States, Hawaii   869 studies
    United States, Idaho   818 studies
    United States, Illinois   6212 studies
    United States, Indiana   3657 studies
    United States, Iowa   2036 studies
    United States, Kansas   2274 studies
    United States, Kentucky   2415 studies
    United States, Louisiana   2750 studies
    United States, Maine   783 studies
    United States, Maryland   7328 studies
    United States, Massachusetts   6054 studies
    United States, Michigan   4682 studies
    United States, Minnesota   3940 studies
    United States, Mississippi   1193 studies
    United States, Missouri   4533 studies
    United States, Montana   974 studies
    United States, Nebraska   2119 studies
    United States, Nevada   1529 studies
    United States, New Hampshire   925 studies
    United States, New Jersey   4027 studies
    United States, New Mexico   1305 studies
    United States, New York   9235 studies
    United States, North Carolina   5975 studies
    United States, North Dakota   908 studies
    United States, Ohio   6503 studies
    United States, Oklahoma   2321 studies
    United States, Oregon   2908 studies
    United States, Pennsylvania   7221 studies
    United States, Rhode Island   1470 studies
    United States, South Carolina   3195 studies
    United States, South Dakota   749 studies
    United States, Tennessee   4202 studies
    United States, Texas   8958 studies
    United States, Utah   2079 studies
    United States, Vermont   956 studies
    United States, Virginia   3615 studies
    United States, Washington   4253 studies
    United States, West Virginia   849 studies
    United States, Wisconsin   2940 studies
    United States, Wyoming   127 studies
Uruguay   26 studies
Uzbekistan   1 study