people overestimated the impact of screening

For example, a review in 2009 found that mammography screenings reduced the number of breast cancer deaths
from five women in one thousand to four.The absolute risk reduction was about .1%.But the relative risk reduction
from 5 cases of cancer mortality to four is 20%.Based on reports of this higher number,people overestimated the impact of screening.To see why the difference between the two ways of expressing risk matters,let’s consider the hypothetical example of a drug that reduces heart attack risk by 40%.