evidence-based public health (1)

8/13/2019 Evidence-Based Public Health (1)

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Evidence-based Public Health

Richard Taylor, PhD, MPH


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Learning Objectives

Explain the steps in evidence-based public

health process.

Describe a public health problem in terms

of morbidity and mortality.

Describe the public health approach to

identify contributory causes of disease or

other conditions and establish the efficacy

of an intervention.


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Learning Objectives (cont.)

Describe the process of grading evidence-

based recommendations.

Use an approach to identify options for

intervention based on when, who, and

how.

Explain the role that evaluation plays in

establishing effectiveness as part of

evidence-based public health.


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Implementation

Recommendations

Problem

Etiology


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Describe a Health Problem

What is the burden of diseasein terms of

morbidityand mortalityand has it changed

over time?

Are there differences in the distribution ofdisease(person, place, time) and can these

differences generate ideas or hypotheses about

the diseases etiology?

Are the differences or changes used to suggest

group associationsartifactual or real?


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Rates

Incidence: measures the chances of

individuals to developa disease during a

particular time period

Prevalence: measures the proportion of

individuals who havethe disease at a

point of time (or during a time period).


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Incidence Rate

# of newcases of a disease over a period of time

# of people in the at-risk population

Often expressed per 10,000 or per 100,000

Expressed using a time period

=


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Control of infectious diseases


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Prevalence Rate

# living with a particular disease

# in the at-risk population

Usually describes a point in time

Can use a period of time (periodprevalence)

Good for describing the total burden orimpact of the health problem in thepopulation at a given time


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Relationship between Prevalence

and Incidence

prevalence = incidence x duration of disease


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Mortality Rates

Type of incidence that measures the rates

of death in a population

Cause of death is classified using

International Classification of Diseases or

(ICD codes)


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Artifactual Changes in Rates

Changes in the interest in identifying the

disease

Changes in the ability to identify the

disease

Changes in the definition of the disease


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Age-adjusted death rates for total cardiovascular

disease, diseases of the heart, coronary heart disease,

and stroke, by yearUnited States, 19001996


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Group-level Associations

Determined using Ecologic studies or

Population comparisons

Associations at a group level may not hold

true at the individual level

May lead to hypothesis generationand

further study to determine the existence of

associations at the individual level


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Implementation

Recommendations

Problem

Etiology


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Etiology: Contributory cause

REQUIREMENTS

Cause is associated withthe effect at the individual

level

Cause precedes theeffect in time

Altering the cause, altersthe effect

STUDY DESIGNS

Cross-Sectional

Case-Control, Retrospective

Cohort, Prospective

Randomized Clinical Trials

Natural Experiments


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Hills Criteria for determining a

causal association

1. Strength

2. Consistency

3. Specificity

4. Temporal relationship (Temporality)5. Biological gradient (Dose-response relationship)

6. Plausibility (Biological plausibility)

7. Coherence

8. Experiment

9. Analogy (Consideration of alternate explanations)


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Implementation

Recommendations

Problem

Etiology


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Recommendations

What works to reduce the health impact?

Built on evidence from studies of

interventions Summaries of the evidence of what works

to reduce the health impact


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Evidence-based Recommendations

Criteria 1:

Quality of evidence Good

Fair

PoorCriteria 2

Magnitude of the impact(Net Benefit) Substantial

Moderate

Small

Negative/zero

Overall RecommendationsAMust

BShould

CMay

DDont IIndeterminant, insufficient,

dont know

Other considerations Cost


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Implementation

Recommendations

Problem

Etiology


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Implementation

When: timing of the intervention Primary

Secondary

tertiary

Who: individuals targeted for the intervention Vulnerable groups

Entire population

How: process of implementing interventions

Information (Education) Motivation (incentives)

Obligation (requirements)


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Natural History of Disease

Period of

susceptibility

Subclinicaldisease

Clinical disease Recovery,

disability or death

PRIMARY

PREVENTIONSECONDARY

PREVENTION

TERTIARY

PREVENTION

Exposure

Pathologicchanges

Onset ofsymptoms

Usual time ofdiagnosis


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EVALUATE, EVALUATE, EVALUATE

Magic bullets are rare

Did the intervention work?

How well did it work? How useful were strategies involving

combinations of approaches?


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Questions?


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The 2-by-2 table

Yes No Total

Yes a b a+b

No c d c+d

Total a+c b+ d a+b+c+d

Outcome

Exposure

Prevalence or cumulative incidence= a/(a+b) among exposed

= c/(c+d) among unexposed

= (a+c)/(a+b+c+d) among total population

evidence-based public health (1)

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