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HSS4303B – Intro to Epidemiology

classes.deonandan.com/hss4303. HSS4303B – Intro to Epidemiology. Mortality Rates, et al. Mortality. Death rates. Mortality Rates. the number of deaths (in general, or due to a specific cause) in some population, scaled to the size of that population, per unit time

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HSS4303B – Intro to Epidemiology

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

  2. Mortality • Death rates

  3. Mortality Rates • the number of deaths (in general, or due to a specific cause) in some population, scaled to the size of that population, per unit time • typically expressed in units of deaths per 1000 individuals per year

  4. The crude death rate, the total number of deaths per year per 1000 people. The crude death rate for the whole world is currently about 8.24 per 1000 per year (according to the current CIA World Factbook.) The perinatal mortality rate, the sum of neonatal deaths and fetal deaths (stillbirths) per 1000 births. (WHO -> 22 weeks pregnancy until 7 days of life) The maternal mortality rate, the number of maternal deaths due to childbearing per 100,000 live births. The infant mortality rate, the number of deaths of children less than 1 year old per 1000 live births. The child mortality rate, the number of deaths of children less than 5 years old per 1000 live births. The standardised mortality rate (SMR)- This represents a proportional comparison to the numbers of deaths that would have been expected if the population had been of a standard composition in terms of age, gender, etc. The age-specific mortality rate (ASMR) - This refers to the total number of deaths per year per 1000 people of a given age (e.g. age 62 last birthday).

  5. Infant, neonatal, and postneonatal mortality rates: United States, 1940-2005 (Wikipedia)

  6. Google public data.

  7. Selected leading causes of death, by sex in Canada

  8. Where Do We Get These Data? • Registries • Surveys/Studies • Surveillance

  9. How Do We Get This Data? • Surveillance • The monitoring of diseases in order to establish patterns of progression • Two types: • Active • Going out and looking for diseases • Passive • Sitting back and waiting for the diseases to be noticed

  10. Active or Passive? • Breast cancer screening programme • Notifiable disease registry Active Passive Why do we need surveillance?

  11. Example: crude data from the Canadian Injuries Surveillance System: Leading causes of death due to injury, 2004 -passive system based on automatic processing of death certificates and hospital charts

  12. Example: Canadian Notifiable Disease Surveillance Report, June 2007 Active system requiring doctors to call the government when certain illness arise (Ontario is blank because no data was available from Ontario in June/2007)

  13. Last Thing: Ecological Studies • Remember the ecological fallacy?

  14. Ecological Study • the unit of analysis is a population rather than an individual • Very crude • Often draw associations between occupation, environment and disease • Considered to be “hypothesis generating” rather than “hypothesis testing” • Ie, they don’t answer questions, just ask more

  15. Ecological Study • Eg, a comparison of saccharine use time trends with time trends of bladder infections • Eg, geographical distribution of farm animals compared with geographical clustering of asthma cases • Eg, study that showed a period with increasing internet cable connections was correlated with a decrease in sexual assaults

  16. Ecological Studies • Cheap • Easy • Suggestive • Fun • dangerous

  17. 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

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

  19. 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?

  20. 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

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

  22. 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%

  23. 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

  24. 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%

  25. 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%

  26. 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?

  27. (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.

  28. Proportionate mortality Rate/Ratio

  29. 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%

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

  31. 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?

  32. 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?

  33. Early and Late Mortality

  34. 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.

  35. 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.

  36. 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.

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

  38. 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

  39. Mortality rates and proportionate mortality rates

  40. Which disease is more serious?

  41. 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?

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

  43. 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

  44. 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?

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