EPIB301_W3L1_Keralis (solutions)

Epidemiologic Measures of Morbidity and Mortality (Part 2)

Overview

  • This section covers key epidemiologic measures including incidence, prevalence, rates, and adjusted rates.

Page 2: Roadmap

  • Key topics include:

    • Incidence and prevalence

    • Recap of previous concepts

    • Practice examples

    • Relationship between incidence and prevalence

    • Different types of rates:

      • Crude rates

      • Specific rates and proportional mortality ratios

      • Adjusted rates

Page 3: Incidence and Prevalence

  • Fundamental measures used to assess disease frequency in populations.

Page 4: Definitions

Prevalence

  • Definition: Frequency of existing cases of a disease in a population during a specified period of time.

  • Importance: Indicates the burden of disease in the total population.

Incidence

  • Definition: Frequency of new cases of a disease in a population during a specified period of time.

  • Importance: Reflects the risk of new disease onset among at-risk populations.

Page 5: Incidence Calculation Practice

  • Scenario: Alikalia, Sierra Leone population: 3,254.

  • July 2, 2014:

    • 212 patients infected

    • 25 deaths

    • 10 recoveries with immunity

    • 12 new cases

  • Incidence rate options (per 100,000):

    • Calculating incidence: # of new cases / total at-risk population.

Page 6: Prevalence Calculation Practice

  • Population: 3,254.

  • Existing cases reported:

    • 212 infected

    • 25 deaths

    • 10 recoveries

    • 12 new cases

  • Prevalence percentage options to calculate:

    • Prevalence: # of cases in population / total population.

Page 7: The Bathtub Model

  • Conceptual model illustrating:

    • Spout: New cases entering (Incidence)

    • Level of water: Prevalence

    • Drain: Cases leaving the population (recovery or death).

Page 8: Factors Affecting Prevalence

  • Increase prevalence factors:

    • Higher incidence

    • Longer disease duration

    • In-migration of cases

    • Out-migration of healthy individuals

  • Decrease prevalence factors:

    • Lower incidence

    • Shorter disease duration

    • Out-migration of cases

    • In-migration of healthy individuals

Page 9: Rates

  • Introduction to epidemiological rates.

Page 10: Types of Rates in Epidemiology

  • Crude Rate: Summary rate for the entire population.

  • Specific Rate: Rate focused on a subgroup.

  • Adjusted Rate: Value adjusted for different demographic characteristics.

Page 11: Comparison of Deaths

  • Death counts and population sizes:

    • London: 4,000 deaths, 800,000 population.

    • Paris: 6,000 deaths, 600,000 population.

Page 12: Crude Rate Definition and Implications

  • Definition: Summary rate based on the total population.

    • Numerator: Frequency of disease.

    • Denominator: Population size at risk.

  • Advantages: Simple calculation.

  • Disadvantages: May misrepresent actual risk due to demographic variations.

Page 13: Crude Mortality Rates Calculation Practice

  • Objective: Calculate crude mortality rates for London and Paris.

  • Formula: Crude mortality rate = (Number of deaths / Reference population) * 100,000.

Page 14: Solution to Crude Mortality Rates

  • London: 500 deaths per 100,000.

  • Paris: 1,000 deaths per 100,000.

  • Conclusion: Paris has a higher crude mortality rate.

Page 15: Infant Mortality Rate

  • Special mortality rate indicator, expressed per 1,000 live births.

Page 16: Infant Mortality Rate Calculation Practice

  • Case: 384 infant deaths out of 40,410 live births.

  • Formula: Infant mortality rate = (Number of deaths <1 year / live births) * 1,000.

Page 17: Solution for Infant Mortality Rate

  • Calculation reveals: 9.5 infant deaths per 1,000 live births.

Page 18: Case Fatality Rate Definition

  • Definition: Rate of deaths among diagnosed individuals with a disease.

Page 19: Case Fatality Rates Calculation Practice

  • Example: Evaluate cholera case fatality rates in London and Paris.

Page 20: Case Fatality Rate Calculation Solution

  • London: 10% case fatality rate.

  • Paris: 20% case fatality rate.

  • Conclusion: Paris has a higher case fatality rate.

Page 21-28: Specific Rates

Types of Specific Rates

  • Age-specific rates: Rates within defined age groups.

  • Sex-specific rates: Rates calculated according to gender.

  • Cause-specific rates: Rates specific to a cause of death.

Practice Examples

  • Various scenarios to calculate specific rates based on demographic data.

Page 29: Proportional Mortality Ratio (PMR) Definition

  • Definition: Deaths due to a specific cause divided by total deaths in a population.

Page 30: PMR Calculation Practice

  • Objective: Calculate PMRs for typhus in London and Paris.

Page 31: PMR Calculation Solution

  • London PMR: 40% of deaths due to typhus.

  • Paris PMR: 30% of deaths due to typhus.

  • Conclusion: London has a higher PMR.

Page 32: Adjusted Rates Definition and Importance

  • Adjusted rates account for demographic variances to allow fairer comparisons across populations.

Page 35-37: Adjusted Rates Example

  • Crude vs adjusted rates comparison for diabetes death rates in New Mexico vs Sierra County.

  • Adjusted rates revealed different risk implications than crude rates alone.

Page 38: Population Age Distribution

  • Comparisons of population age distributions revealing different health risk profiles for regions.

Page 39: Closing Remarks

  • Reminder of the upcoming class and scheduled homework assignments.