Whenever it is not possible for a scientist to do controlled
experiments, then they use observational research and opinion based research.
Observational research actually requires collecting of data without performing
an experiment. These observations often lead to biased and inaccurate results. This
is one of the major pitfalls of observational research. Opinion based research
often requires a scientist to design an experiment and collect the data. The
data collected are mostly arbitrary in nature, but it definitely gives a
direction for further progress.
