Why sophistication? What is Epi? - SJSU

Why sophistication? 4/22/2010

Comp P H Stats 1

4/22/2010 Why sophisticated biostat? 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


What is Epi?

Epi = “methodological backbone” of public health

Epidemiology → “study of distribution and

determinants of health and disease…, and application…”


Does Scientific Public Health Work?

Life Expectancy

Objective

interpretation


Epidemiologic Transition

20th century shift from acute, contagious diseases

to chronic lifestyle diseases

Leading Causes of Death

CerbrovascularDiarrhea3

NeoplasmsTuberculosis2

Heart diseasePneumonia / influenza1

19901900

Why have the causes of morbidity and mortality shifted? (That’s a different question…)


Reasons for Epi.Transition• First half of twentieth century (advances in childhood)

– Industrialization → standard of living

– Birth control & maternal education (first half of 20th century)

– Improved nutrition

– Sanitation and vector control

• Second half of 20th century (advances in middle age)– Improvements in lifestyle

– Improved medical education

– Specific medical treatment (e.g, antibiotics, anti-hypertensives, improved surgical safety…)

Doll, R. (1992). Health and the environment in the 1990s. Am J Public

Health, 82(7), 933-941.

Surtout, Messieurs, point de zele. – Talleyrand


Age-Adjusted Death Rates, US

objectivity …please


Comp P H Stats 2


Demographic Transition

(a) ↓ mortality at early and middle

age

(b) ↓ fertility

(c) ↑ longevity


Modern Epidemiology• Shift in morbidity and

mortality (“epi. transition”) mandate shift in epimethods

• Advent of “modern epidemiology”

• Focus on multiple factors acting together (confounding and interaction)

4/22/2010 Why sophisticated biostat? 9Gerstman 9

Rothman on CauseDefinition 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

Ken Rothman(contemporary epidemiologist)

Disease results from the Disease results from the

cumulative effects of multiple cumulative effects of multiple

causes acting together causes acting together

((causalcausal interactioninteraction))


Types of Causes

• 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

A given disease can have multiple sufficient mechanisms


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”


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?

Is cancer genetic or environmental?Is cancer genetic or environmental?

genetictraityellow

corn


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Contagion Theory vs. Miasma

Theory

Competing 19th Century Theories of Cause & Prevention

[and a lesson in confounding]

A lesson from the past


Competing 19th Century Theories


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 (19th Public Health) Movement


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

(1813–1858)


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)


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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”

1807 - 1883


Farr’s View of Cholera


Farr's graph of cholera and elevation

Farr’s theory ⇒ atmospheric condition prevalent in low-lying areas allowed non-living decomposing organic matter to become poisonous and enter the lungs.

Farr figure showing Y = elevation (0 to 350 feet) and X = Cholera mortality per 10000


Modern analysis of Farr’s data

Regression of cholera

incidence on mean elevation

above sea level

log-log scales

r = −.99


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


What was wrong with Farr’s analysis?

My “bad”!

Miasma theory (and

the Sanitation Movement) was ultimately discredited

In 1885 (about 40

years later), Farr adopted the contagion theory.


Comp P H Stats 5


Lesson’s Learned• Simplistic interpretations of data are

detrimental to the public’s health• We MUST consider multiple variables

acting together (confounding and interaction)

• 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

Why sophistication? What is Epi? - SJSU

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