Why sophistication? What is Epi? Epidemiologic Transition

Transcription

1 Why sophistication? If our motive is to manipulate, our communication and our leadership in general will prove to be ineffective over time. -- Stephen R. Covey Epidemiology study of distribution and determinants of health and disease, and application Epi = methodological backbone of public health What is Epi? 4/22/2010 Why sophisticated biostat? 1 4/22/2010 Why sophisticated biostat? 2 Does Scientific Public Health Work? Life Expectancy Objective interpretation Epidemiologic Transition Leading Causes of Death Pneumonia / influenza Heart disease Tuberculosis Neoplasms Diarrhea Cerbrovascular 20 th century shift from acute, contagious diseases to chronic lifestyle diseases 4/22/2010 Why sophisticated biostat? 3 Why have the causes of morbidity and mortality shifted? (That s a different question ) 4/22/2010 Why sophisticated biostat? 4 Reasons for Epi.Transition First half of twentieth century (advances in childhood) Industrialization standard of living Birth control & maternal education (first half of 20 th century) Improved nutrition Sanitation and vector control Second half of 20 th century (advances in middle age) Improvements in lifestyle Improved medical education Specific medical treatment (e.g, antibiotics, anti-hypertensives, improved surgical safety ) Age-Adjusted Death Rates, US objectivity please Doll, R. (1992). Health and the environment in the 1990s. Am J Public Health, 82(7), Surtout, Messieurs, point de zele. Talleyrand 4/22/2010 Why sophisticated biostat? 5 4/22/2010 Why sophisticated biostat? 6 Comp P H Stats 1

2 Demographic Transition (a) mortality at early and middle age (b) fertility (c) longevity 4/22/2010 Why sophisticated biostat? 7 Modern Epidemiology Shift in morbidity and mortality ( epi. transition ) mandate shift in epi methods Advent of modern epidemiology Focus on multiple factors acting together (confounding and 4/22/2010 Why sophisticated biostat? 8 Rothman on Cause Definition of cause Any event, act, or condition preceding disease or illness without which disease would not have occurred or would have occurred at a later time Disease results from the cumulative effects of multiple causes acting together (causal Ken Rothman (contemporary epidemiologist) Gerstman 4/22/2010 Why sophisticated biostat? 9 Necessary cause found in all cases Contributing cause needed in some cases Sufficient cause the constellation of necessary & contributing causes that make disease inevitable in an individual Types of Causes A given disease can have multiple sufficient mechanisms 4/22/2010 Gerstman Why sophisticated biostat? 10 Causal Complement (Causal Pie) Causal complement the set of factors that completes a sufficient causal mechanism Example: tuberculosis Necessary agent Mycobacterium tuberculosis Causal complement Susceptibility 4/22/2010 Gerstman Why sophisticated biostat? 11 Yellow Shank Illustration Yellow shank disease occurs only in susceptible chicken strains fed yellow corn What would a farmer think if he started feeding yellow corn to a susceptible flock? What would a farmer think if he added susceptible chickens to a flock being fed yellow corn? Is yellow shank disease environmental or genetic? yellow corn Is cancer genetic or environmental? genetic trait 4/22/2010 Gerstman Why sophisticated biostat? 12 Comp P H Stats 2

3 A lesson from the past Competing 19 th Century Theories Contagion Theory vs. Miasma Theory Competing 19 th Century Theories of Cause & Prevention [and a lesson in confounding] 4/22/2010 Why sophisticated biostat? 13 4/22/2010 Why sophisticated biostat? 14 Miasma Theory Miasma bad air Noxious vapors & atmospheric conditions spontaneously propagate the non-living cholera poison from ordinary organic decay and decomposition Cholera poison inhaled Dominant theory of Sanitation (19 th Public Health) Movement 4/22/2010 Why sophisticated biostat? 15 Contagion Theory Cholera agent is free-living Multiplies within the host Water-borne transmission Spread via fecal contamination Patho-physiology oral ingestion diarrhea fluid loss smudging of blood asphyxiation John Snow ( ) 4/22/2010 Why sophisticated biostat? 16 Water-borne cholera transmission Snow Died in Obscurity Initially known as a great surgeon BUT died in obscurity WHY? his views on the etiology of cholera were in opposition to the prevailing public health mood at the time (Lilienfeld 2000, Winkelstein 1995) 4/22/2010 Why sophisticated biostat? 17 4/22/2010 Why sophisticated biostat? 18 Comp P H Stats 3

4 William Farr (Founding Sanitarian) First registrar of a national morbidity and mortality reporting system Father of public health statistics Subscribed to a part miasma / part contagion theory /22/2010 Why sophisticated biostat? 19 Farr s View of Cholera 4/22/2010 Why sophisticated biostat? 20 Farr's graph of cholera and elevation Farr s theory atmospheric condition prevalent in lowlying areas allowed nonliving decomposing organic matter to become poisonous and enter the lungs. Farr figure showing Y = elevation (0 to 350 feet) and X = Cholera mortality per Modern analysis of Farr s data r =.99 Regression of cholera incidence on mean elevation above sea level log-log scales 4/22/2010 Why sophisticated biostat? 21 4/22/2010 Why sophisticated biostat? 22 What was wrong with Farr s analysis? What was wrong with Farr s analysis? The relationship between elevation (exposure) and cholera (disease) was confounded by proximity to contaminated water sources (extraneous confounder ) Correlation causation Miasma theory (and the Sanitation Movement) was ultimately discredited In 1885 (about 40 years later), Farr adopted the contagion theory. My bad! 4/22/2010 Why sophisticated biostat? 23 4/22/2010 Why sophisticated biostat? 24 Comp P H Stats 4

5 Lesson s Learned Simplistic interpretations of data are detrimental to the public s health We MUST consider multiple variables acting together (confounding and John Snow brilliance = his understanding of inter-relations between social and environmental factors with sound pathological principals Farr was ultimately willing to change his mind when confronted with overwhelming evidence Farr was a good scientist Many items in this piece were derived from The John Snow Archive & Research Companion 4/22/2010 Why sophisticated biostat? 25 Comp P H Stats 5