1. Instructor Resource Chapter 4 Copyright © Scott B. Patten, 2015. Permission granted for classroom use with Epidemiology for Canadian Students: Principles, Methods & Critical Appraisal (Edmonton: Brush Education Inc. www.brusheducation.ca).

2. Chapter 4. Specialized mortality rates and composite measures of disease burden

3. Objectives Define and interpret key specialized measures of mortality: cause-specific mortality rate, age- and sex-specific mortality rate, perinatal mortality rate, infant mortality rate case-fatality rate. Define and interpret composite health indicators: QALYs and DALYs. Describe the role of these rates and indicators in monitoring population health.

4. Cause-specific mortality This is among the oldest quantifiers of mortality (e.g., 17 th century “Bills of Mortality” in England). It is most commonly expressed as a proportion or rate (but can also be a count). Its numerator expresses the number dying of a specific cause Its denominator expresses the midyear population at risk. Note: as the midyear population represents person- time at risk, this ratio can be regarded as a rate.

5. Cause-specific mortality (continued) Usually, information about the cause of death comes from medical certificates of death. These are recorded in provincial mortality databases and then shared nationally. “Death Certificates” record underlying causes, immediate causes, and the intermediate steps (antecedent causes). The WHO ICD system is used to code the causes.

6. Cause-specific mortality (continued) Usually, information about the cause of death comes from medical certificates of death These are recorded in provincial mortality databases and then shared nationally “Death Certificates” record underlying causes, immediate causes and the intermediate steps (antecedent causes)

7. Top 10 causes of death in Canada (1) malignant neoplasms (cancer) (2) heart disease (3) cerebrovascular diseases (stroke) (4) chronic lower respiratory diseases (5) accidents (6) diabetes (7) Alzheimer disease (8) influenza and pneumonia (9) suicide (10) kidney disease

8. Cause-specific mortality (continued) Usually, information about the cause of death comes from medical certificates of death These are recorded in provincial mortality databases and then shared nationally “Death Certificates” record underlying causes, immediate causes and the intermediate steps (antecedent causes)

9. Cause-specific mortality (continued) Mortality rates are a kind of incidence rate. Causes of death that are: Sudden Unexpected Nonmedical are investigated by medical examiners, providing another source of data that can be used in epidemiological studies.

10. Age- and sex-specific mortality These are calculated within specified age and sex strata. Specialized examples include: perinatal mortality rate infant mortality rate

11. Perinatal mortality Perinatal death is death of a child less than one week of age (0 to 6 days) or a stillbirth of 28 or more weeks gestation. Perinatal mortality rate is perinatal deaths (numerator) divided by the number of total births (denominator), which consist of live births and late fetal deaths.

12. Infant mortality Infant death is death of child less than 1 year of age. Infant mortality rate is infant deaths in a year (numerator) divided by the live birth count for the same year.

13. Case fatality rates This is really a proportion that is labelled by convention as a rate. The numerator expresses people who die from the disease. The denominator expresses people with a disease. Note: this parameter only makes sense for a disease with a defined risk interval (e.g., an infectious or toxin- induced disease in an outbreak). An incidence proportion without a defined risk intervals is otherwise not meaningful.

14. Survival proportions and relative survival ratios The proportion of people with a cancer who survive for 5 years is an example of a survival proportion. The relative survival ratio uses the proportion of comparable people without the cancer who are expected to survive the time interval (usually 5 years). The relative survival ratio is recommended by the Canadian Cancer Society.

15. Potential years of life lost (PYLL) Causes of death are strongly related to age. Most of the top causes of death kill mostly older people—a reality not reflected in crude mortality rates. PYLL (usually called “YPLL” in the US) calculates the potential years of life lost. In Canada, PYLL is based on the number of years of potential life not lived when a person dies before age 75.

16. PYLL (continued) For example, a death from a disease that occurs at age 65 results in 10 PYLL. A death after age 75 results in no PYLL. PYLL can be expressed as a number or rate. The rate uses a person-time denominator. When this is done, the person-time in the rate is the midyear population of those younger than 75.

17. Quality adjusted life years (QALY) QALY is pronounced “qually.” Quality of life refers to a person’s self-appraisal of their own health. These are often assessed as “utility” in scales such as the Health Utilities Index (HUI) or EQ-5D. Typically, perfect health means utility = 1. A state comparable to death means utility = 0. Every disease leads to a state that is between these values. The impact of a disease or treatment on health can be weighed as QALYs gained or lost.

18. Disabiltiy-adjusted life-years (DALY) DALY is pronounced “dally.” It is calculated as the sum of years lived with disability and (potential) years of life lost. The concept of disability is broad—and is usually estimated using utility-defining strategies (e.g., “standard gamble” methods). Mainly used by the Global Burden of Disease project, but also in other burden of disease studies. (By contrast, QALYs tend to be used in health economic studies.)

19. Proportional mortality ratios These are falling out of use—they are mainly of historical interest. They were popular when only “numerator” mortality data (death counts) were available. They are calculated as the number of deaths due to a specific cause (numerator) divided by the total number of deaths (denominator).

20. End