Mortality Measures in Epidemiology PDF

BSc Medical Sciences: Epidemiology Assistant Prof. Dr. Soza Th. Baban Introduction and Review In Week 3, we discussed: 1. Measures of morbidity, including incidence rates, cumulative incidence, attack rates, prevalence, and disease surveillance. 2. Understand and calculate the case fatality ra...

BSc Medical Sciences: Epidemiology Assistant Prof. Dr. Soza Th. Baban Introduction and Review In Week 3, we discussed: 1. Measures of morbidity, including incidence rates, cumulative incidence, attack rates, prevalence, and disease surveillance. 2. Understand and calculate the case fatality rate (CFR) and explain its importance in assessing disease outbreaks. 3. Interpret and analyse spot maps to identify disease patterns. Learning objectives By the end of this session, students should be able to: 1. Define key mortality measures including mortality rates, case-fatality, and proportionate mortality and understand their differences. 2. Calculate and interpret proportionate mortality. 3. Compare mortality rates across populations with different demographics. 4. Understand application of mortality rate in public health. Let’s go through each of these points in detail!  Crude Mortality (or Death) Rate The Crude Mortality Rate (CMR) is the simplest measure of mortality. It represents the total number of deaths in a population over a given period, regardless of the cause of death. Formula: (Number of deaths / Total population) * 1000 It is important to recognize that the crude death rate summarizes the effect of two factors: A. population composition B. age-specific death rates (which reflect the probability of dying)  Crude Mortality (or Death) Rate Population Crude Mortality Rate per 1000 Popultation (A) White 9.95 Example: (B) Black 7.35 The above table shows the crude death rates of two populations, A and B by Race, State of Maryland, USA 2015: The crude death rate for population A is 9.95 per 1000. The crude death rate for population B is 7.35 per 1000. Apparently, population B appears healthier, than population A. Death rates by age per 1000 population Race All ages 85 year year year year year year year year year year year A 9.95 4.06 0.21 0.11 0.64 1.29 1.73 3.62 7.68 16.45 45.39 138.7 B 7.35 11.25 0.43 0.78 1.14 1.74 2.23 5.09 11.14 21.55 49.49 124.45  Cause-Specific Mortality (or death) Rate The Cause-Specific Mortality Rate (CSMR) focuses on the number of deaths due to a specific cause in a population. The specific death rates may be: (a) cause or disease specific - e.g., tuberculosis, cancer, accident; (b) related to specific groups e.g., age-specific, gender-specific, age and gender specific, etc. CSMR can also be made specific for many other variables such as income, religion, race, housing, etc. Specific death rates can help us to identify particular groups or groups "at- risk", for preventive action. No of deaths from specific cause ×1,000 Total population Example: If 100 people die from heart disease in a population of 100,000: (100 / 100,000) * 1000 = 1 per 1,000 people die from heart disease. Cause-Specific Mortality (or death) Rate  Proportional mortality rate Proportionate mortality rate shows the percentage of deaths in a population that are due to a specific cause, relative to all deaths. It is sometimes useful to know what proportion of total deaths are due to a particular cause (e.g., cancer) or what proportion of deaths are occurring in a particular age group (e.g., above the age of 50 years). Proportional mortality rate expresses the "number of deaths due to a particular cause (or in a specific age group) per 100 (or 1000) total deaths". (a) Proportional mortality from a specific disease Number of deaths from the specific disease in a year ×100 Total deaths from all causes in that year  Proportional mortality rate The proportionate mortality from cardiovascular disease in the United States in 2015 is defined as follows: In other words, of all deaths in the United States, what proportion was caused by cardiovascular disease? Proportional mortality from cardiovascular diseases in the US in 2015 (%) Number of deaths from cardiovascular disease in the US in 2015 ×100 Total deaths in the US in 2015  Proportional mortality rate (b) Under-5 proportionate mortality rate Number of deaths under 5- years of age in the given year ×100 Total number of deaths during the same period (c) Proportional mortality rate for aged 50 years and above Number of deaths of persons aged 50 years and above ×100 Total deaths of all age groups in that year  Proportional mortality rate This figure shows proportionate mortality from heart disease by age group. In each age group, the full bar represents all deaths (100%), and deaths from heart disease are indicated by the dark blue portion. We see that the proportion of deaths from heart disease increases with age. However, this does not tell us that the risk of death from Deaths from heart disease as a percentage of deaths from all causes, by age group, United States, 2014. heart disease is also increasing. This is demonstrated in the following examples.  Case Fatality Rate (CFR) CFR measures the severity of a disease by calculating the percentage of people who die from it. What percentage of people who have a certain disease die within a certain time after their disease was diagnosed? It is useful for understanding how deadly an outbreak is. Formula: CFR =(Number of Deaths /Number of Confirmed Cases x100 Example: If there are 10 deaths out of 200 confirmed cases of a disease, the CFR is: CFR = (10/200) x 100 = 5%. Number of individuals dying during a specified period of time after disease onset or diagnosis ×100 No. of individuals with the specified disease  Comparison of Mortality rate with Case-Fatality in the same year Assume a population of 100,000 people of whom 20 are sick with disease X, and in 1 year, 18 of the 20 die from disease X Assume that in a population of 100,000 persons, 20 have 18 Mortality rate from disease X. = 0.00018, or 0.018% disease X= 100,000 In 1 year, 18 people die from that disease. The mortality is very low (0.018%) because the disease is rare; however, 18 Case-fatality rate from = 0.19, or 90% once a person has the disease X= 20 disease, the chances of his or her dying are great (90%). Homework: 1) What is the difference between case-fatality and a mortality rate? (provided with example) 2) What is the difference between mortality rate and proportionate mortality? (provided with example) 3) What is the importance of measuring mortality rate? Why look at mortality? Explain with an example Refer to Gordis Epidemiology book, page 68 to 75.  Survival rate It is the proportion of survivors in a group, (e.g., of patients) studied and followed over a period (e.g., a 5-year period). It is a method of describing prognosis in certain disease conditions. Survival experience can be used as a yardstick for the assessment of standards of therapy. The survival period is usually reckoned from the date of diagnosis or start of the treatment. Survival rates have received special attention in cancer studies. Total number of patients alive after 5 years Survival rate = ×100 Total number of patients diagnosed or treated  Challenges in Mortality Measurement Mortality data is crucial for public health, but there are challenges in ensuring accurate measurement: 1. Underreporting: Some deaths may go unrecorded, especially in under- resourced areas. 2. Misclassification: Errors in identifying the correct cause of death can skew mortality statistics. 3. Inconsistent data: Different countries and regions might use different criteria for measuring mortality. 4. Population differences: Differences in age, sex, or location can make mortality rates difficult to compare.  Application of Mortality Measures Mortality measures are essential tools in public health for understanding how diseases impact different populations. These measures help public health officials: Prioritize interventions by identifying diseases that contribute most to mortality. Allocate resources effectively by understanding disease burden. Evaluate the success of public health interventions by monitoring trends in mortality. Inform health policy decisions based on accurate mortality data.  Recap and Q&A Today, we covered essential mortality measures: Crude Mortality Rate Cause-Specific Mortality Rate Case Fatality Rate Proportionate Mortality We also discussed challenges in mortality measurement and how these measures are applied in public health. Feel free to ask any questions or share your thoughts! Preparation for Next Session For next session, please: 1. Read Chapter 5 (Pages 94-105) from 'Gordis Epidemiology'. 2. Be prepared to discuss how these measures are used to evaluate population health outcomes.