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1142 Studies found for: subjects AND Double-blind AND Petersburg

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Map Legend
Region Name Number of Studies
World 1,142
Africa [map] 283
Central America [map] 153
East Asia [map] 437
Japan 194 [studies]
Europe [map] 851
Middle East [map] 345
North America 998
Canada [map] 514 [studies]
Mexico 346 [studies]
United States [map] 958 [studies]
North Asia [map] 854
Pacifica [map] 381
South America [map] 449
South Asia [map] 162
Southeast Asia [map] 233

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Studies with no locations are not included in the counts or on the map.

Studies with multiple locations are included in each region containing locations.