– – , , , 2 • , • , 2. C (Basic/pure research) • , , 1. , (investigative reporting) 2. (descriptive research 3. (causal/explanatory research) 4 • • • • , – , – , – : 3. • , . • : – , • : • : • : • • , • 14 • : – – , • , • . • ? • . - (Intervention, • . - Population based Gross -sectional • . - Ecological study ? • , , . ? • . - Clinical trial • . - Cohort / descriptive • . - Ecological study 2 . ? • . - Cohort /descriptive • . - Ecological study – – – “”- • , , . • Rothman, 1986 • •