CDC EIS,1999:London Fog-Instructor's Guide Page 7 Question 5:Estimate the number of excess deaths in 1952/1953. est method for calculating excess mortality is to specify the period of interest.then subtract the expected number of deaths from the observed number of deaths for each week,and sum up. nude the excess deaths tor the weeks ending Nov.2 and Dec.6.since they are The steps are as follows 1.First.calculatexpecumber of deaths for each week.In this setting,use the mean number of de tieaegomR6ra6isicano0ie1setngs,heepectednumber 4 Calculate the upper from the upper limit to get calculate the exc te upper ct the observed number of deaths Add the excess deaths for the entire time period Excess above standard 5-yr mean Excess Week ending 1952/1953 5-year mean 5-yr mean on SL above 2 SD Noy 15 727 154 2 Nov.22 1,699 1,726 ,154 29 4.703 1.893 2.81 2.556 1. 728 Jan.3 2977 2275 Jan.10 2.634 2,239 612 395 3.463 TOTAL EXCESS: 5.505 3,284 What are some pos ible expla for ee ortality in 1952-1953? Answer 6 include e contained in the fog(air pollutant) nts agent introduced by animals or fa hers participating in the Smithfield Show other e.g. CDC / EIS, 1999: London Fog - Instructor's Guide Page 7 Question 5: Estimate the number of excess deaths in 1952/1953. Answer 5 The simplest method for calculating excess mortality is to specify the period of interest, then subtract the expected number of deaths from the observed number of deaths for each week, and sum up. (You would not include the excess deaths for the weeks ending Nov. 29 and Dec. 6, since they are “pre-epidemic”.) A second method, more complicated but more scientifically rigorous, is to compute excess mortality as the number of deaths that exceed the upper 95% confidence limit for expected deaths for a given week. The steps are as follows: 1. First, calculate the expected number of deaths for each week. In this setting, use the mean number of deaths for that week, based on previous years. In other settings, the expected number may be based on a more complicated formula or a statistical model. 2. Calculate the standard deviation. 3. Calculate the upper 95% confidence limit as the mean + 2 standard deviations. 4. If the observed number of deaths exceeds the upper limit, subtract the observed number of deaths from the upper limit to get calculate the excess. 5. Add the excess deaths for the entire time period. Excess above standard 5-yr mean Excess Week ending 1952/1953 5-year mean 5-yr mean deviation + 2 SD above 2 SD Nov. 8 1,593 1,746 — 110 1,966 — Nov. 15 1,565 1,727 — 154 2,035 — Nov. 22 1,699 1,726 — 214 2,154 — Nov. 29 1,902 1,737 [165] 241 2,219 — Dec. 6 2,062 1,849 [213] 238 2,325 — Dec. 13 4,703 1,893 2,810 127 2,147 2,556 Dec. 20 3,138 1,952 1,186 229 2,410 728 Dec. 27 2,234 1,822 412 364 2,550 — Jan. 3 2,977 2,275 702 652 3,579 — Jan. 10 2,634 2,239 612 395 3,463 — TOTAL EXCESS: 5,505 3,284 Question 6: What are some possible explanations for the excess mortality in 1952-1953? Answer 6 Possibilities include: • a substance contained in the fog (air pollutant) • influenza • traffic accidents • zoonosis - e.g., an agent introduced by animals or farmers participating in the Smithfield Show • other