Consider a group of 1,000 newborn infants. 100 infants were born with serious birth defects and 20 of these 100 died during the first year of life. 90 of the 900 remaining infants without any birth defects also died during the first year of life.

Calculate the prevalence of serious defects in this population at the time of birth.

Calculate the overall cumulative incidence of mortality in this population.

Calculate the cumulative incidence difference in mortality between infants born with serious birth defects and without.

State in words your interpretation of the cumulative incidence difference calculated in part c.