In a study to determine the incidence of a chronic disease, 150 people were examined at the end of a 3-year period. twelve cases were found, giving an incidence rate of 8%. fifty other members of the initial cohort could not be examined; 20 of these 50 members could not be examined because they died. does this loss of subjects to follow-up represent a source of bias that may have affected the study results? answer yes or no and provide an explanation.