Consider a group of 1,000 newborn infants. One hundred (100) infants were born with serious birth defects, and 20 of these 100 died during the first year of life. Ninety (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 risk difference (or attributable risk) in mortality between infants born with serious birth defects and without.

Name two ways to eliminate bias in a study