classes. deonandan. com/hss 4303 HSS 4303 B – 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 • typically expressed in units of deaths per 1000 individuals per year
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).
Infant, neonatal, and postneonatal mortality rates: United States, 1940 -2005 (Wikipedia)
Google public data.
Selected leading causes of death, by sex in Canada 1997 Number All causes % Total Males Females Rate 1 215, 669 100. 0 658. 7 844. 0 521. 6 Cancers 58, 703 27. 2 181. 5 229. 7 148. 5 Diseases of the heart 57, 417 26. 6 173. 0 230. 8 129. 7 Cerebrovascular diseases 16, 051 7. 4 47. 8 52. 8 43. 9 Chronic obstructive pulmonary diseases and allied conditions 9, 618 4. 5 29. 0 44. 5 20. 1 Unintentional injuries 8, 626 4. 0 27. 6 37. 8 17. 9 Pneumonia and influenza 8, 032 3. 7 23. 7 31. 5 19. 2 Diabetes mellitus 5, 699 2. 6 17. 4 20. 6 14. 8 Hereditary and degenerative diseases of the central nervous system 5, 049 2. 3 15. 0 16. 7 13. 9 Diseases of arteries, arterioles and capillaries 4, 767 2. 2 14. 3 19. 5 10. 6 Psychoses 4, 645 2. 2 13. 6 13. 3 13. 4 Suicide 3, 681 1. 7 12. 0 19. 5 4. 9
Where Do We Get These Data? • Registries • Surveys/Studies • Surveillance
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
Active or Passive? • Breast cancer screening programme • Notifiable disease registry Why do we need surveillance? Active Passive
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
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)
Last Thing: Ecological Studies • Remember the ecological fallacy?
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
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
Ecological Studies • • • Cheap Easy Suggestive Fun dangerous
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
Crude Death Rate Deaths per year per 1000 people ->
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?
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
Specific mortality rates ate r lity orta cm n re hild i ecif sp C te ra ality e g Lun ate r ality t r hild C c spe en if leuk ic em mor ia ca sp cer n t mor cific
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%
Case fatality rate • 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
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: 18/100000 = 0. 018% The case-fatality rate of disease X is: 18/20 = 90%
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? 45000/4500000 = 1% What is cause specific mortality rate for AIDS? 30000/4500000 = 0. 7% What is case-fatality rate for AIDS? 30000/650000 = 4. 6%
Mortality rates and incidence rates • Mortality is an index of the severity of a disease Incidence? • Mortality can also be an index of the _______ – Therefore mortality can be used an index of disease incidence 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
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. (The fraction of all deaths from a given cause in the study population divided by the same fraction from a standard population) A tool for investigating causespecific risks when only data on deaths are available.
Proportionate mortality Rate/Ratio
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? 45000/4500000 = 1% What is cause specific mortality rate for AIDS? 30000/4500000 = 0. 7% What is case-fatality rate for AIDS? 30000/650000 = 4. 6% What is the PMR? 30000/45000 = 66. 7%
Mortality rates in two communities Table 4 -2. Comparison of Mortality Rate and Proportionate Mortality: I. Deaths from Heart Disease in Two Communities, A and B Community A Mortality rate from all causes Proportionate mortality from heart disease Mortality rate from heart disease Community B 30/1, 000 15/1, 000 10% 20% 3/1, 000 What is the risk of dying from heart disease? Community A Community B Mortality rate from all causes 3% 1. 5% Proportionate mortality from heart disease 10% 20% Mortality rate from heart disease 0. 3%
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?
Mortality rate from all causes Proportionate mortality from heart disease Mortality rate from heart disease Raywatville Gomesland
Mortality rate from all causes Proportionate mortality from heart disease Mortality rate from heart disease Raywatville Gomesland 30/1, 000 15/1, 000 10% 20% 3/1, 000
Raywatville Gomesland Mortality rate from all causes 3% 1. 5% Proportionate mortality from heart disease 10% 20% Mortality rate from heart disease 0. 3% 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?
Early and Late Mortality
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. 1. 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. 2. 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.
Example: Early Mortality Rate of Morbidly Obese Patients after Tracheotomy by Ilaaf Darrat, 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.
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 survive more than 5 years after diagnosis of childhood cancer and to evaluate causes of death in fatal cases. RESULTS. Overall late mortality was significantly lower 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 no increase in rates of death due to cancer treatment.
Consider a population of 1000 people. Compute: A) case-specific mortality rates for each period B) PMRs for each period Cause of death Early Period Mortality Rate Later Period Proportionate Mortality Rate Proportionate Mortality Heart disease 40/1000 % 80/1000 % Cancer 20/1000 % All other causes 20/1000 % All deaths 80/1000 100% 120/1000 100%
Consider a population of 1000 people with the following deaths Consider a population of 1000 people. Compute: A) case-specific mortality rates for each period B) PMRs for each period Cause of death Early Period Mortality Rate Later Period Proportionate Mortality Rate Proportionate Mortality Heart disease 40/1000 50% 80/1000 67% Cancer 20/1000 25% 20/1000 17% All other causes 20/1000 25% 20/1000 17% All deaths 80/1000 100% 120/1000 ~100%
Mortality rates and proportionate mortality rates
Disease specific mortality rate PMR CFR Dumbass Disease 6% Nosepickery 14% 64% 26% 13% Which disease is more serious? 1%
Comm A Comm B Mortality rate from all causes 20/1, 000 10/1, 000 30% Proportionate mortality from heart disease Mortality rate from heart disease Rate of death Proportion 6/1, 000 3/1, 000 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?
Burden of Disease How would you measure a population’s “burden”?
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
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?
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
YPLL for children YPLL before the age of 65 years for children and young adults younger than 20 years of age
Use of YPLL • YPLL assists in – Establishing research and resources priorities – Surveillance of temporal trends in premature mortality – Evaluating the effectiveness of program intervention
Another Option for Disease Burden QALYs – “Quality Adjusted Life Years” – www. jr 2. 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
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?
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
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!
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
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 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….
Life Expectancy Life expectancy in the USA, stolen from www. imminst. org
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
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
–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
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
Current Global Burden of Disease (DALYs, 1999) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 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
Projected Global Burden of Disease (DALYs, 2020) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 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
Survival
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
Observation of each patient begins at diagnosis (time = 0), and continues until one of the following outcomes occurs: death, survival for 5 years, or follow-up ceases (the subject is "censored"). A patient is censored when follow-up ends prior to death or completion of a full period of observation. Follow-up could end for one of several reasons: (1) the patient decides to discontinue participation, (2) the patient is "lost" to follow-up, or (3) the study ends. Five of the six people under observation (N = 6) survive at least 2 years. Thus, the 2 -year survival is 5/6= 0. 83= 83%
Specifying Length of Survival • 1, 2, 5 years are standard, but it can be anything • For example, prostate cancer has a much higher one year overall survival rate than pancreatic cancer, and thus has a better prognosis.
We Can Break It Down Further • Example from the textbook (p 23) • 5 year survival rate for leukemia is 19% – But if you break it down by age: • <65 yrs -> 5 year survival is 31% • =>65 yrs -> 5 year survival is 4% Are the older folks dying of cancer or other causes? Does this statistic capture this difference? Does it matter?
Why do we measure Survival? • What does it tell us? It’s a measurement of disease severity
Relative Survival Rate • RSR • Ratio of survival rate of disease in question, divided by the survival rate of the general population (preferably not including those who have the disease) • Eg RSR of cancer at 2 years = (% of cancer patients who are alive @ 2 years) / (% of general population who are alive @ 2 yrs) Tells us whether the disease shortens life • Why is this important? Eg, The overall 5 -year relative survival rate for 1999 -2005 from 17 SEER geographic areas was 89. 1%. Five-year relative survival rates by race were: 90. 3% for white women; 77. 9% for black women.
E. G, Health Canada’s definition of RSR for prostate cancer http: //www. statcan. gc. ca/pub/82 -401 -x/2002000/considerations/hlt/4064233 -eng. htm
Also from Health Canada:
Cause-Specific Survival Rate • Cause-specific survival (CSS) is a term that denotes the chances of death due to a particular condition (or cause) at a particular point of time. It takes care to exclude death due to unrelated causes in patients suffering from the cancer in question. This means that 15% of The 5 -year cause-specific these patients are survival for stage IIA estimated to die directly Hodgkin lymphoma is due to the Hodgkin disease 85% when treated with by 5 years. The remaining ABVD followed by 85% are either alive or have involved field radiation. died due to other unrelated causes.
Compute 5 year Survival Rates for Cancer (hit by truck) (by cancer) 5 year survival rate = (A-D)/A = (6 -2)/6 = 67% 5 year cause specific survival rate = (6 -1)/6 = 83%
Problems with mortality data • Information on mortality is obtained from death certificates • Deaths are coded according to the underlying cause – Which is defined as the disease or injury which initiated the train of morbid events leading directly or directly to death or circumstances of accident or violence which produced the fatal injury – The underlying cause therefore excludes information pertaining to the immediate cause of death, contributory causes and those that intervene between the underlying and immediate causes of death • Some causes of death have better validity than others
Cause of death from a death certificate
ICD classification on death certificates • Deaths are coded by ICD classification • Drop in diabetes related deaths in 1949 were caused by changes in classification codes • Prior to 1949 the policy was to include diabetes as cause of death anywhere on the certificate lead to diabetes being mentioned on the death certificate • After 1949 only death certificates on which the underlying cause of death was listed as diabetes were coded as a death from diabetes
Changes in death rates from diabetes caused by changes in classification
Changes in the definition of disease • In 1993, a new definition of AIDS was introduced • These changes resulted in a rapid rise in the number of reported cases
AIDS cases in the US from 1984 -2000
Causes of death in the early 20 th century Table 4 -6. Some Causes of Death That Were Reported on Death Certificates in the Early 1900 s "Died suddenly without the aid of a physician" "A mother died in infancy" "Deceased had never been fatally sick" "Died suddenly, nothing serious" "Went to bed feeling well, but woke up dead"
Homework • P. 28, questions 1 -7
Abstract Assignment • • Due Jan 29 at 11: 59 pm Submit via email to: hss 4303@gmail. com Do not CC it to the professor or the TA The subject line of the email should be your name and student number, nothing else. – “Oleg Hammerstein 1234567” • All described on the website: – Classes. deonandan. com
Abstract Assignment • Make sure you include the “contribution statement” • You have a choice of 5 topics, but you have some leeway to explore something within a given topic – E. g. , if you want, specify women only, or in a certain region or over a certain time
Abstract Assignment • Adhere to the 300 word limit • Use peer-reviewed papers as sources • If you must use a website, limit it to ONE only, and make it a major registry • This tests: – Your ability to find pertinent information – Your ability to read that information – Your ability to summarize the important aspects of that information
Abstract Assignment • The topic does NOT have to match the topic of your poster • Giving me what I ask for is “adequate” • Being specific, showing a compelling writing style, finding the major sources, being accurate. . . All the nice extras. . . Are what make it “excellent”
Abstract Assignment • This is an individual assignment • Do not use any in-text citations, but do list the 3 -5 references that you used • Even so, if you lift substantial text verbatim from a source, we will notice and it will constitute plagiarism – So don’t be tempted!
Abstract Assignment • Imagine I asked you, “Tell me about hepatitis in Canada. ” What would you tell me? • The audience is an educated non-specialist, so don’t assume we know (non-epidemiological) jargon, but do assume that we went to a good school
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