The Lancet authors based their calculations on an overall, post-invasion, excess mortality rate of 7.8/1000/year. "Pre-invasion mortality rates were 5.5 per 1000 people per year (95% CI 4.3–7.1), compared with 13.3 per 1000 people per year (10.9–16.1) in the 40 months post-invasion."[1] See Table 3 in the Lancet article.[2] The population number used in the calculation is reported in the Lancet supplement:[2] "Mortality projections were applied to the 2004 mid-year population estimates (26,112,353) of the surveyed areas (which exclude the governorates of Muthanna and Dahuk, which had been omitted through misattribution) to establish the mortality projections."