Causal Hypotheses, Mill's Canons, Observational Study Designs (Cohort Studies, Case-Control) & Sampling

“Ifa factor is common to a number of different circumstances in which a disease is present, then the factor may be the cause of the disease”, and such a method of formation of "Causal Hypothesis” is known as:

Ifa group exposed to the factors is compared with a group not exposed to the factors with respect to the development of a disease, then such type of epidemiological study is known as:

When sampling units have not the equal chances of being selected, then that sampling strategy is known as