In what circumstances do scientists use observational research and opinion based research?

Observational research is used in early stages of scientific research because it gives us a rough estimate and a general idea at what variables should be look at when we're trying to discover something new.

Opinion based research works through the same principle, someone who is an expert in a field can tell us what does he think could be researched next. Both of these pieces of information are only used as a general idea and not as something definitive.

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