In a study, group of smokers followed up for 10 years to find incidence of a cancer. What type of study design is this?

Types of coho study: 1. Prospective/Concurrent Coho Begin in present and continue to future Outcome has not yet occurred at the time the investigation begins 2. Retrospective/Historical coho Outcomes have occurred before sta of investigation Investigator goes back in time to select study groups from existing records of past employment , up to the present 3. Ambidirectional/mixed coho Combination of retrospective and prospective coho studies