Why don't scientist say that they have proven their hypothesis true?

Awaiver of the requirement for documentation of informed consent may be granted when: the investigator has no convenient place to store signed consent forms separate from the research datathe only record linking the subject and the research is the consent document and the principal risk is a breach of confidentiality.potential subjects might find some of the research questions embarrassing, personal, or intrusivethe subjects are literate in their own language; however, they do not read, write, or speak english

New zoya is a country of english-speaking people and has a very profitable economy. which of the following countries is most likely to be the closest to new zoya in terms of cultural distance? sulfura, which has a very profitable economy and where people speak sulfuran valyria, where people speak english and have a low standard of living danver, which has the same wealth and per capita income as new zoya novalandia, which is located close to new zoya and is easily accessible by road

Feathers wings and the hollow bones of birds are examples of