Perspectives on Teaching

1. The Biology of Public Health Transmission: Explain biological concepts related to PH clearly to achieve mastery of content Perspectives on Teaching Developmental: Application to PH problems Developmental: Structured thinking. Moving from simple to complex thinking & problem solving. Assessing validity. Introduction to Epidemiology Transmission: Explain concepts.

2. Transmission: …have mastery of content and represent it accurately and efficiently. … provide clear objectives, adjust pace, answer questions, clarify, summarize, etc. Apprenticeship: …reveal inner workings of skilled performance & translate it into accessible language and an order set of tasks. Progression from simple to complex. Must know what learners can do on their own…. Developmental: Primary goal is to help learners develop increasingly sophisticated cognitive structures for comprehending content. Key is two skills: a) effective questioning that challenges learners to move to more complex forms of thinking, and b) “bridging knowledge”: questions, problems, cases, examples. Nurturing: via knowledge that they can succeed in learning if they try; achievement is a product of their own efforts and ability. Good teachers create a climate of caring and trust and setting challenging, but achievable goals and providing encouragement and support.

3. My Rules of Engagement • Think of yourself as a more experienced learner. • Be a leader, not a boss. Have a plan. Listen. • Be yourself; don’t try to be funny. • You must earn their trust. Never humiliate a student. • Don’t cram content. Leave time to discuss.

4. Use stories to engage and show relevance. • Use problems to engage and challenge. • Change pace & methods. • Visualize concepts; reduce use of text on slides. • Reflect on your teaching before and after class.

5. Comments on ‘Engaging’ Use of PowerPoint

6. ODDS RATIO “THE RATIO OF THE ODDS OF HAVING THE TARGET DISORDER IN THE EXERIMENTAL GROUP RELATIVE TO THE ODDS IN FAVOUR OF HAVING THE TARGET DISORDER IN THE CONTROL GROUP (IN COHORT STUDIES OR SYSTEMATIC REVIEWS) OR THE ODDS IN FAVOUR OF BEING EXPOSED IN SUBJECTS WITH THE TARGET DISORDER DIVIDED BY THE ODDS IN FAVOUR OF BEING EXPOSED IN CONTROL SUBJECTS (WITHOUT THE TARGET DISORDER).”

7. Controls Cases The Odds Ratio A case-control study comparing odds of exposure. Hepatitis Yes No 18/1 7/29 Odds Ratio = 18 7 Yes Ate at Deli? = 75 No 1 29 Hepatitis cases were 75 times more likely to have eaten at the Deli. 19 36 Odds of exposure 18/1 7/29

8. Beginning With a Pair-Share Discussion of a Problem-An Embedded Flash Animation-Checking Understanding With an Audience Response System

9. Measuring Disease Frequency

10. The mayor of your town was startled to learn that there are 3 people who were recently diagnosed with hepatitis A in his neighborhood. He is concerned that this may just be the tip of the iceberg, and he is wondering if this signals an epidemic. He wants your help in assessing the magnitude of the problem. What information do you need in order to assess: • How big the problem is in town, • Whether there is an epidemic starting. • How the problem in your town compares to that of neighboring towns.

11. Population A group of people with some common characteristic (age, race, gender, place of residence). Examples: • Residents of Boston • Members of Blue Cross/Blue Shield • Postmenopausal women in Massachusetts • Coal miners in Pennsylvania • Adolescents in U.S. Sample: Residents of Marshfield, MA 19 who got hepatitis 38 who did not

12. Dynamic Population: membership can be transient. Example:Residents of Boston Fixed population: membership is permanent and defined by some event. Example:Survivors of the atomic bomb blasts in Japan

13. Basic Concepts • Ratio • Proportion • Rate

14. Women Women Men Men Ratio A number obtained by dividing one number by another. Example:the ratio of women to men in a class # women 120 = 8 # men 15 1 A ratio doesn’t have any dimensions or units. It just indicates the relative magnitude of the two entities. = =

15. Proportion A type of ratio that relates a part to a whole; often expressed as a percentage (%) . Example:proportion of women in a class # women = 120 = 88.9% total # students 135 Women Men Women

16. Proportion A type of ratio that relates a part to a whole; often expressed as a percentage (%) . Example:Theproportion of students who developed a respiratory infection during the semester. # with colds 45 33.3% total # students 135 = =

17. Rate A type of ratio in which the denominator also takes into account the dimension of time. Example: 120 miles in 2 hours 120 miles = 60 miles per hr. 2 hours Example: 60 gallons in 3 hours 60 gal. = 20 gal. per hr. 3 hours

18. Rate A type of ratio in which the denominator also takes into account the dimension of time. Example:the rate of myocardial infarctions (heart attacks) in a study population taking low dose aspirin. 254.8 per 100,000 person-years

19. Counts of Disease If events aren’t recorded, there is no way to detect trends.

20. HIV+ people in our town 2001 5 2002 7 2003 10 2004 3 2005 5 2006 19 Counts of Disease The simple count of HIV+ people provides the basis for significant discussions among city officials and health care providers. Simple counts are essential to public health planners and policy makers by providing a direct measure of the need for resources for specific problems.

21. Our Town 75 Next Town 35 But Count Data Alone Are Insufficient for Making Comparisons HIV+ Is HIV more of a problem in our town? Obviously, you need to take into account the time frame and size of each population.

22. Measures of Disease Frequency Prevalence(a proportion) Incidence • Cumulative incidence (a proportion) • Incidence rate (a rate)

23. Prevalence The proportion of a population that has disease at a giventime. The focus is on existing disease at a specific time, not the development of new cases.

24. Point Prevalence The proportion of a population or group that has disease at a specific “point” in time. • The focus is on existing disease at a specific point in time. • Imagine you took a snapshot of a class and labeled those suffering from hay fever or other allergies with a red “A” . A A A A A

25. 310 had cataracts Eye exam survey of 2,477 people Period Prevalence The proportion of a population that has disease during a given period of time. x x xx x x x xxx x x 1979 1980 1981 Prevalence = 310 (cataracts) 2,477 (total) = .125 = 12.5%

26. Prevalence of HIV in MA in 2003 8,263 HIV+ = 0.00145 = 0.145% = 14.5 per 10,000 Total MA population = 5.7 million in 2003 Express it this way.

27. Incidence Frequency ofnewcases during aspan of timein people “at risk”. X X X X X X X X X X Numerator: # new cases during a span of time. Denominator: includes only people “at risk”. The focus is on measuring the probability of developing disease during a span of time.

28. Prevalence versus Incidence 2006 2007 2008 2009 2010 2003 2004 2005 X X XX X XX X X X XX Prevalence In 2003 = 0.00145% Incidence: Frequency of new cases during a span of time in people at risk. Prevalence is the probability of having disease at a point in time. Incidence is the probability of developing disease during a span of time.

29. Incidence Cumulative incidence (a proportion) Incidence rate (a true rate) • Both focus on # new cases of disease • (numerator) during a period of observation. • The difference is the way they handle time.

30. x xxx x xx x xx xx x x x xx x x x x x x Cumulative Incidence Example: 25 colds in a class of 50 during spring semester. • A proportion • A fixed block of observation time • Assumes complete follow-up for all subjects. • You don’t know the precise “time at risk” for each person. • The time period is described in words (“… during spring semester.”) Jan. 2007 (50 students) May 2007 (45 students) CI = 25/50 = 50% during spring semester

31. TB Incidence in Boston During 2005? In reality, people are moving in and out of Boston, and some will die (& no longer be members of the population). But there is no way to know the details of this. The best we can do is assume that the number of people in the population stays the same and they are always at risk.

32. TB Incidence in Boston During 2005? We need to assume the population is fixed, i.e. all people were followed for the entire block of time. CI = # new cases 2005 est. pop. size Cumulative incidence (a proportion)

33. Cumulative Incidence of AIDS in MA During 2004 CI = 523 new AIDS cases = 9.2/100,000 Population at risk: about 5.7 million from 1/1/04 to 1/31/04

34. X o o X o o o o X o o X X X X X X X X X Here, the outcome of interest is relief of pain. Which has greater rate of relief? Which has greater proportion of relief? New drug Old drug 1 2 3 4 5 6 7 8 9 10 Hours

35. Incidence Rate of HIV Seropositivity in Prostitutes IR = 4 new AIDS cases = 0.15 = 15/100 P-Yrs 26 person-yrs Sum = 26 yrs

36. Incidence Rate Total # new cases Total amount of disease-free observation time for a group

37. X = when they got disease Incidence Rate Time at Risk Subject A- B- C- D- E- F- G- H- I- J- K- L- 8.3 x 11.0 14.0 14.0 10.2 x 3.0 12.0 7.0 10.0 3.0 9.0 x 6.2 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 Total =107.7 person-yrs CI = 3 12 over 14 yrs IR = 3 = 28 107.7 p-ys 1000 p-yrs

38. X o o X o o o o X o o X X X X X X X X X CI versus IR? Which has greater rate of relief? Which has greater proportion of relief? CI = 6/10 = 60% over 10 years IR = 6/49 p-yrs = 12.2/100 P-yrs New drug CI = 6/10 = 60% over 10 years IR = 6/85 p-yrs = 7/100 P-yrs Old drug 1 2 3 4 5 6 7 8 9 10

39. wgt kg hgt m2 41 177,356 23.1 57 194,243 29.3 56 155,717 36.0 67 148,541 45.1 85 99,573 85.4 The Nurse’s Health Study Association? Risk of Non-fatal Myocardial Infarction Obesity rate of MI per 100,000 P-Yrs (incidence) # MIs (non-fatal) person-years of observation BMI: <21 21-23 23-25 25-29 >29 126 lb @ 5’6” = 21 175 lb @ 5’6” = 29

40. Incidence provides a way of measuring the risk of becoming diseased. 2006 2007 2008 2009 2010 2003 2004 2005 X X XX X XX X X X XX Incidence: Frequency of new cases during a span of time in people at risk. Incidence is the probability of developing disease during a span of time.

41. Summary –Measures of Disease Frequency Prevalence (a proportion) = People# People with disease at a point in time Total People # People in the study population Cumulative Incidence (a proportion) = People# new cases in a specified period Total People # People (at risk) in the study population Incidence Rate (a rate) = People# new cases of disease People-Time Total observation time in a group at risk

42. Attack Rate (a cumulative incidence) The proportion of exposed people who develop disease. (Not really a rate; it’s a special type of cumulative incidence.) TB exposure Passengers on Honolulu to Baltimore flight within 2 rows of index case Positive TB tests

43. Case Fatality Rate The proportion of diseased people who die - in this case 2/6 = 33%. (Again, not a rate, but a special type of cumulative incidence.) SARS cases A measure of the severity or risk of dying from the disease if you have it. Example:, 33% of people who got SARS died.

44. Prevalence Depends on Incidence & Duration of Disease Prevalence = Incidence x Average Duration of Disease P = I x D If the prevalence, incidence, and average duration of disease have been relatively constant, this relationship can be used to predict the effects of changing incidence or average duration.

45. Average Duration of Disease Affects Prevalence Prevalence = Incidence x Average Duration of Disease P = I x D Not surprisingly, brief, acute illnesses such as viral gastroenteritis do not have high prevalence, because they don’t last long. In contrast, diseases like diabetes have greater prevalence because they aren’t rapidly fatal, but there is not real cure; they are just controlled.

47. Calculating the Mean Duration of Disease If Prevalence = Incidence x Avg. Duration, then Avg. Duration = Prevalence Incidence • Example:Lung cancer: If incidence = 46 new cancers per 100,000 P-Yrs (i.e., in a population of 100,000 you expect 46 cases per year), and prevalence = 23 per 100,000 population. • What is the average duration of lung cancer? Since D = P/IR then D = 23/100,000 persons = 0.5 years 46/100,000 person-years Conclusion:People with lung cancer survive an average of 6 months from diagnosis to death.

48. Use of an Audience Response System to: • Assess understanding, • Reinforce concepts, • Identify & clarify misconceptions, and • Build confidence. • (And have fun.)

49. PH officials used surveillance data to determine the number of new cases of tuberculosis in Boston during 2008, and they computed the frequency of new TB cases using census data as an estimate of the population size in 2008. What measure of disease frequency did they calculate? • Prevalence • Cumulative incidence • Incidence rate • Attack rate • Case fatality rate

50. Which measure of disease frequency best describes the percentage of men found to have previously undiagnosed prostate cancer at autopsy? • Prevalence • Cumulative incidence • Incidence rate • Attack rate • Case fatality rate