Outside of the budget and resource issues that others above have pointed out, it would be interesting to consider conducting a clinical study depending on where the issue you are tackling is most prevalent. For example, if you are conducting clinical trails on a drug that targets malaria, you can argue that you should conduct the clinical trial on subjects in the Sub-Saharan Africa region where malaria is the major burden of disease. The results would provide more substance and intended results as opposed to conducting a clinical trial on a subject within high income developed country.