HSS4303B – Intro to Epidemiology

1. classes.deonandan.com/hss4303 HSS4303B – Intro to Epidemiology Jan 18, 2010 – Mortality Rates, et al

2. Epidemiologic measures • Mortality • Case fatality rates • Years of potential life lost (YPLL) • Survival • Disability assisted life year (DALY) • Disability Adjusted Life Expectancy (DALES) • And other goodies

3. Crude Death Rate Deaths per year per 1000 people ->

4. Cancer related deaths What is the trend in the number of deaths from 1900 to 2000? What is the trend in the risk of death from 1900 to 2000?

5. Mortality rate Denominator must include all potential persons eligible to be included in the numerator Mortality rates can be calculated for specific groups of people such as children, age specific, postmenopausal, females, boys less than 10 years, etc. Specific rates Age specific Disease specific Cause specific

6. Specific mortality rates Children specific mortality rate Lung cancer specific mortality rate Children specific leukemia mortality rate

7. Case Fatality Rate • Case fatality (CF) is the risk of death from a certain disease • CF = Number of deaths / Number of diagnosed patients with the disease Ebola Virus is among the deadliest viruses with a case fatality rate of roughly 90%

8. Mortality rate Denominator is the entire population at risk of dying from the disease (with or at risk) Measures risk of dying from the disease Case-fatality rate Denominator is limited to those who already have the disease Measures severity of disease Measures benefits of new therapy Case fatality rate

9. Mortality rates and case-fatality rates Assume a population of 100,000 people of which 20 are sick with disease X and in one year 18 of the 20 die from the disease Mortality rate in that year as a result of disease X: The case-fatality rate of disease X is: 18/100000 = 0.018% 18/20 = 90%

10. If a population of a country is 4.5 million and if in a given year 45000 deaths from all causes occurred in that country of which 30,000 deaths were AIDS related among 650,000 HIV infected people. What is the mortality rate from all causes? What is cause specific mortality rate for AIDS? What is case-fatality rate for AIDS? 45000/4500000 = 1% 30000/4500000 = 0.7% 30000/650000 = 4.6%

11. Mortality rates and incidence rates • Mortality is an index of the severity of a disease • Mortality can also be an index of the _____________ • Therefore mortality can be used an index of disease incidence • Mortality is a good index of _______________ when: • The case fatality rate is high • The duration of disease is short • Mortality is a good index of incidence for pancreatic cancer because the survival is short and fatality rate is high Incidence? Incidence?

12. (The fraction of all deaths from a given cause in the study population divided by the same fraction from a standard population) Proportionate Mortallity Rate or Ratio (PMR) The number of deaths from a specific cause in a specific period of time per 100 deaths from all causes in the same time period. A tool for investigating cause-specific risks when only data on deaths are available.

13. Proportionate mortality Rate/Ratio

14. If a population of a country is 4.5 million and if in a given year 45000 deaths from all causes occurred in that country of which 30,000 deaths were AIDS related among 650,000 HIV infected people. What is the mortality rate from all causes? What is cause specific mortality rate for AIDS? What is case-fatality rate for AIDS? What is the PMR? 45000/4500000 = 1% 30000/4500000 = 0.7% 30000/650000 = 4.6% 30000/45000 = 66.7%

15. Mortality rates in two communities What is the risk of dying from heart disease?

16. Mortality rates in two communities Raywatville and Gomesland are two adjacent communities. Raywatville has 1000 damn sexy residents. Gomesland has 1000 dignified residents. In Raywatville in 2007, 30 people died from all causes, while in the same year 15 died in Gomesland. That same year, in each community 3 of the deaths were due to heart disease. A) compute crude mortality rate s for both communities B) Compute PMR for heart disease both communities C) Compute specific mortality rate for heart disease for both communities D) What is the risk of dying of heart disease in each community? E) Which community has the greater risk of dying of heart disease?

19. D) What is the risk of dying of heart disease in each community? E) Which community has the greater risk of dying of heart disease?

20. Early and Late Mortality

21. Let’s say there’s an intervention to try and prevent death caused by a disease. We distinguish between “early” and “late” mortality rates, to account for the lag in the intervention having an effect. The early mortality rate, the total number of deaths in the early stages of an ongoing treatment, or in the period immediately following an acute treatment, divided by those at risk. The late mortality rate, the total number of deaths in the late stages of an ongoing treatment, or a significant length of time after an acute treatment, divided by those at risk.

22. Example: Early Mortality Rate of Morbidly Obese Patients after Tracheotomy by IlaafDarrat, MD, Kathleen Yaremchuk, MD The Laryngoscope, Volume 118 Issue 12, 2009, Pages 2125 - 2128 Objectives: To 1) determine the early mortality rate (within 30 days) of morbidly obese patients after tracheotomy; 2) determine the difference between the mortality rate after tracheotomy of morbidly obese patients and patients who are not morbidly obese; and 3) determine the difference between the mortality rate after tracheotomy adjusted for case mix index (CMI) of morbidly obese patients and patients who are not morbidly obese.

23. Example Decreasing Late Mortality Among Five-Year Survivors of Cancer in Childhood and Adolescence: A Population-Based Study in the Nordic Countries by Moller et al Journal of Clinical Oncology, Vol 19, Issue 13 (July), 2001: 3173-3181 PURPOSE: To assess the risk of death in patients who survivemore than 5 years after diagnosis of childhood cancer and toevaluate causes of death in fatal cases. RESULTS. Overall late mortality was significantlylower in patients treated during the most recent period of time,1980 to 1989, compared with those treated from 1960 to 1979(hazard ratio, 0.61; 95% CI, 0.54 to 0.70), and there was noincrease in rates of death due to cancer treatment.

24. Consider a population of 1000 people. Compute: • case-specific mortality rates for each period • PMRs for each period

25. Consider a population of 1000 people with the following deaths • Consider a population of 1000 people. Compute: • case-specific mortality rates for each period • PMRs for each period

26. Mortality rates and proportionate mortality rates

27. Which disease is more serious?

28. Rate of death Proportion Rate of death from heart disease A) What is the risk of death in each community? B) What is the risk of death from heart disease? C) What is the burden of heart disease in each community?

29. Burden of Disease How would you measure a population’s “burden”?

30. Years of potential life lost (YPLL) Is a measure of premature mortality or early death Deaths at a younger age involves a loss of future productive years of life Eg, if you are expected to live to 65 and a disease kills you at age 20, then you have lost 45 years (65-20). So the YPLL for this disease is 45

31. YPLL • Canada, 1993 • injuries killed 10,286 people • Cancer killed 25,687 people • But Cancer affected more young people, and injuries killed more old people • cancer caused 302,585 YPLL • injuries caused 336,593 YPLL Which disease is more serious?

32. YPLL • Obviously you need: • A specific time period • A defined population • A defined life expectancy • YPLL for a population for a disease = sum of all YPLL of individuals lost to that disease

34. YPLL for children YPLL before the age of 65 years for children and young adults younger than 20 years of age

35. Use of YPLL • YPLL assists in • Establishing research and resources priorities • Surveillance of temporal trends in premature mortality • Evaluating the effectiveness of program intervention

36. Another Option for Disease Burden QALYs • “Quality Adjusted Life Years” • www.jr2.ox.ac.uk/bandolier/booth/glossary/QALY.htm • Used to measure both the quality and quantity of life years lived as a result of a medical intervention • QALY = (year lived) x (index) • Index = 0  1 • 0 = death, 1 = perfect health • E.g., new heart valve saves your life, but hinders your quality of life

37. QALY Example • Bob is 50 and has heart disease. He is expected to live for another 10 years. • His is given a special heart stent that extends his life such that he is expected to live till 80 • Because of the stent, he must give up all exertion, which really sucks • It is believed that the stent represents a quality index of 0.6 • How many QALYs did the stent give Bob?

38. QALY Example • Without stent, Bob would have lived 10 years • With stent, Bob lives 30 years (80-50) • Thus, Bob gains 20 years • QALYs = (years gained) x (index) = 20 x 0.6 = 12 years

39. Oh but it doesn’t end there… DALE • “Disability Adjusted Life Expectancy” • Measure life expectancy in a population, shortened to account for quality years lost due to disability • Eg: Japan has one of the world’s highest life expectancies = 81.3 years, computed at birth • But DALE in Japan is 74.5 years!

40. DALEs • Like QALYs, requires agreement on how much a disability “shortens” the quality of one’s life • DALE of an individual = total number of years lived without disability + number of years with disability x (index) Index = 0 -> 1 (just like in QALYs) DALE of a population = sum of DALES of each member

41. Life Expectancy • The expected time remaining to live • Usually given relative to birth • E.g., Presently, life expectancy at birth is 32.6 years in Swaziland and 81 years in Japan • Life expectancy is computed using “life tables”, which means that it will vary depending on what age it is calculated for….

42. Life Expectancy Life expectancy in the USA, stolen from www.imminst.org

43. Life Expectancy What’s the problem with using life expectancy as a gauge of population health? • More ill-health and disabilities, and greater suffering? • Longer period of life in good health? • Does long life = productive life? economics • Some have proposed using “healthy life expectancy” or HLE (meanwhile, TLE=“total life expectancy”) • The expected number of years to be spent in good health • Need to weight different disabilities based on severity

44. And The Grand Daddy of them all… DALYs • “Disability Adjusted Life Year” invented in 1996 • Measure of overall disease burden in a population • www.who.int/healthinfo/boddaly • A DALY is considered a bad thing : • The number of years of productive life lost in a population due to both death and disability

45. DALY = YLL + YLD • YLL = years of life lost in the population due to death from a specific health • YLD = years of productive life lost due to disability, rather than death

46. Why is the DALY so important? • Now we have a measure for the population burden of a disease that accounts for the impact, not only of death, but of morbidity

47. Current Global Burden of Disease (DALYs, 1999) • Acute lower respiratory infections • HIV/AIDS • Perinatal conditions • Diarrhea • Unipolar major depression • Ischemic heart disease • Cerebrovascular disease • Malaria • Traffic injuries • COPD • Congenital abnormalities • TB • Falls • Measles • Anemia Source: WHO, Evidence, Information and Policy, 2000

48. Projected Global Burden of Disease (DALYs, 2020) • Ischemic heart disease • Unipolar major depression • Traffic injuries • Cerebrovascular disease • COPD • Lower respiratory infections • TB • War • Diarrhea • HIV • Perinatal conditions • Violence • Congenital abnormalities • Self-inflicted injuries • Trachea, bronchus and lung cancers Source: WHO, Evidence, Information and Policy, 2000

49. Survival

50. Survival rates • _____________ is the probability of remaining alive for a specific length of time • 1 year and 5 year survival are often used as indicators of the severity of disease and the prognosis • 5 year survival rates for myelocytic leukemia is about 0.14, indicating that about 14% of the patients with acute myelocytic leukemia survive for at least 5 years after diagnosis. • Survival (S) = (A – D) / A where • A is the number of newly diagnosed patients under observation and D is the number of deaths observed in a specified period of time