<prompt> Which among the following is the major practical problem in a coho study?Differential loss of follow upLong duration of studyCan be used only for rare conditionsNone of the above  <response>: Disadvantages of coho studies: Have to follow large numbers of subjects for a long time. They can be very expensive and time consuming. They are not good for rare diseases. They are not good for diseases with a long latency. Differential loss to follow up can introduce bias. 