a study to determine the incidence of an infectious disease, 1000 people were examined at the end of a 1-year period. Two hundred fifty cases were found, giving an incidence rate of 25%. Three hundred other members of the initial cohort could not be examined; 276 of these 300 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? Please answer YES or NO and provide an explanation