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Descriptive Epidemiology: Counting, Rates, and Surveillance

Explore how health-related states or events are distributed in a population through systematic data collection, analysis, and interpretation. Learn about counting, rates, and surveillance systems for drug abuse.

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Descriptive Epidemiology: Counting, Rates, and Surveillance

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  1. Module 1 Overview Context Content Area: Descriptive Epidemiology & Surveillance Essential Question (Generic): How are health-related states or events distributed? Essential Question (Drug Abuse Specific): How is drug abuse distributed? Enduring Epidemiological Understanding: The frequency and distribution of health-related states or events in a population can be determined by systematically collecting, analyzing, and interpreting data. Synopsis In Module 1, students explore how to describe the distribution of health-related states or events. Students begin to uncover and develop the following epidemiological concepts and skills: observing groups of people, counting, the value of a denominator, a case definition, a representative sample, and creating circumstances that encourage truthful responses and protect confidentiality. Lesson 1-1: Counting and Rates Lesson 1-2: Introduction to Surveillance Lesson 1-3: Counting/Describing HIV / AIDS Lesson 1-4: Counting High School Marijuana Use Lesson 1-5: National Survey on Drug Use and Health Lesson 1-6: Other Drug Abuse Surveillance Systems

  2. Module 1 - Descriptive Epidemiology and Surveillance • Lesson 1-1 Counting and Rates • Content • Definitions of epidemiology, descriptive epidemiology, population science • Expressing what is observed in numbers / counts • Adding denominators to increase information from counts: creating ratios, proportions, rates • Getting comfortable with rates • Rates used in epidemiology • Big Ideas • Epidemiology uses population science to describe patterns of disease and health • Counts become more meaningful with a denominator • Denominators allow us to calculate proportions, percentages and rates, and compare different groups • People go in and out of the numerator (incidence versus prevalence) This project is supported by a Science Education Drug Abuse Partnership Award, Grant Number 1R24DA016357-01, from the National Institute on Drug Abuse, National Institutes of Health.

  3. Where are we? Essential Questions Enduring Understandings

  4. Review: Definition of Epidemiology “… the study of the distribution and determinants of health-related states or events in specific populations and the application of this study to the control of health problems.” Gordis 2004

  5. Epidemiology - Study at the Population Level “… the study of the distribution and determinants of health-related states or events in specific populations and the application of this study to the control of health problems.”

  6. Descriptive Epidemiology “… the study of the distributionand determinantsof health-related states or events in specific populations and the application of this study to the control of health problems.”

  7. Descriptive Epidemiology Epidemiologic studies that are concerned with characterizing the amount and distribution of health and disease within a population.

  8. DZ DZ DZ DZ Descriptive Epidemiology Distribution 1 Describe what you observe Express it in numbers

  9. Descriptive Epidemiology Lord Kelvin1824-1907 When you can measure what you are speaking about, and express it in numbers, you know something about it. But when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind.

  10. Epidemiologists Like to Count Things Related to Health What do Epidemiologists count? Numbers of people who get sick Numbers of people who die Numbers of people with a certain health habit Numbers of people with a certain exposure But, epidemiologists do more than count

  11. Real Example Figure 7.2 Dependence on or Abuse of Specific Illicit Drugs in the Past Year among Persons Aged 12 or Older: 2005

  12. Epidemiologists Do More Than Count But, epidemiologists do more than count

  13. Epidemiologists Do More Than Count Town A has 27 new cases of cocaine dependence/abuse in April Town B has 94 new cases of cocaine dependence/abuse in April What do these counts mean about the impact of cocaine dependence/abuse? It depends . . . need a context It depends on the number of people in Towns A and B In other words, it depends on denominators - a basis for comparison

  14. Epidemiology Toolbox Denominators give us context • For example: • Town A has 27 new cases of cocaine dependence/abuse in a population of 1000 • Town B has 94 new cases of cocaine dependence/abuse in a population of 5000 • With a denominator we can now calculate • Proportions • Percentages • Rates

  15. Epidemiology Toolbox: Proportions Numerator # = Proportion # Denominator … when the people in the numerator are included in the denominator

  16. Epidemiology Toolbox: Proportions Town A Numerator Proportion 27/1000 = 0.027 27 1000 Denominator … the proportion of new cases of cocaine dependence/abuse in April in Town A is 0.027

  17. Epidemiology Toolbox: Percentages Numerator # X 100 = Percentage # Denominator … when the people in the numerator are included in the denominator and the decimal is multiplied by 100

  18. Epidemiology Toolbox: Percentages Town B Numerator 94 0.019 X 100 = 1.9% 5000 Denominator … 1.9% of the people in Town B were identified as dependent upon or abusing cocaine in April

  19. Epidemiology Toolbox: Rates Numerator - everyone with the outcome of interest in a given time period = Rate Denominator - everyone at risk for the health outcome of interest, i.e., the population at risk, in a certain time period … when the people in the numerator are included in the denominator, and there is a a time frame

  20. Epidemiology Toolbox: Rates Numerator Rate 0.027 x 1000 = 27 cases per 1000 per month 27 1000 Denominator … the rate of new cases of cocaine dependence/abuse in Town A is 27 cases per 1000 per month

  21. Epidemiology Toolbox: Rates Numerator Rate 0.019 x 1000 = 19 cases per 1000 per month 94 5000 Denominator … the rate of new cases of cocaine dependence/abuse in Town B is 19 cases per 1000 per month

  22. Epidemiology Toolbox: Big Ideas about Rates Because rates can use common denominators, it is easier to compare rates between towns (or other groups) with different population sizes Because rates can specify a time frame, they tell us about the “speed” of a disease

  23. Summary of Proportions, Percentage, Rates

  24. DZ DZ DZ DZ Descriptive Epidemiology Distribution 2

  25. DZ DZ DZ DZ Descriptive Epidemiology Describe what you observe Express what you observe in numbers

  26. DZ DZ DZ DZ Descriptive Epidemiology Distribution 3 Describe what you observe Express what you observe in numbers.

  27. Count Divide Compare Descriptive Epidemiology

  28. Count Divide Compare Descriptive Epidemiology

  29. Getting Comfortable with Rates Review In epidemiology, a rate expresses the impact of a disease or other health-related condition in a defined population in a specified time frame # of health-related events in the population at risk per a defined time period Rate = x K # of people in the population at risk A multiplier or constant such as per 1000 or 100,000 people

  30. Types of Rates in Epidemiology and Public Health One distinction is mortality versus morbidity rates • Mortality - part of “Vital” Statistics • Mortality (national, state and local rates • Natality (such as infant death rates) • Morbidity - unhealthy, state of disease/sickness • Health Surveys • Cancer registries • Infectious disease statistics • Drug abuse surveys Denominators to define population at risk? Remember the Census!

  31. Types of Rates in Epidemiology and Public Health Another distinction is incidence rates versus prevalence rates • Incidence rate = Number of new cases of a disease Total population at risk For a given time period For a given point in time or time period • Prevalence rate = Number of existing cases of a disease Total population

  32. Prevalence Pot Prevalence Pot Recovery In Out Incidence Death Prevalence Pot

  33. Recovery Incidence Death Prevalence Pot Prevalence Pot In Out Recovery Recovery Incidence Death Death Prevalence Pot

  34. Prevalence Pot In 14 Out 27 5 157 27 + 157 - 14 - 5 = 165

  35. Re-Cap • Big Ideas in this Lesson (1-1) • Epidemiology uses population science to describe patterns of disease and health • Counts become more meaningful with a denominator • Denominators allow us to calculate proportions, percentages and rates, and compare different groups • People go in and out of the numerator (incidence versus prevalence) This project is supported by a Science Education Drug Abuse Partnership Award, Grant Number 1R24DA016357-01, from the National Institute on Drug Abuse, National Institutes of Health.

  36. NextLesson (1-2) Population Surveillance

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