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.