Epidemiology for Public Health Practice 5th Edition by Robert Friis,Thomas Sellers

Exercise 3

Two automated blood cell counters are tested twice using a prepared suspension of leukocytes containing 8,000 cells/mm3. The cell counts by device A are 8,400 cells/mm3 the first time and 8,350 cells/mm3 the second. Device B's counts are 8,200 and 7,850 cells/mm3, respectively. Which device (A or B) gives leukocyte counts with greater validity? Which device gives leukocyte counts with greater reliability?