Post on 12-Jan-2016
transcript
Laurie Anderson, PhD, MPH
Centers for Disease Control & Prevention
February 10, 2004
Outline
I. Difference between a literature review and a systematic review
II. Purpose of the Guide to Community Preventive Services: systematic reviews & evidence-based recommendations
III. Steps in carrying out a systematic reviews
IV. An example
The difference between
a literature review and
a systematic review
When making decisions about the choice of an intervention
The body of intervention literature can be quite large, inconsistent, and uneven in quality.
Literature Reviews
A “literature review” has typically been used to provide background information for intervention selection.
These reviews present a group of studies, with
strengths and weaknesses discussed selectively
and informally.
Traditional literature reviews have several shortcomings:
•The process is subjective. There are few formal rules, two reviewers might reach different conclusions.
•Lack explicit criteria for excluding inappropriate or poorly done studies.
Typically a literature review counts the number of studies supporting, or not supporting, an intervention
i.e. positive, negative, or no effect
but ignores sample size, effect size and research design.
This can lead to erroneous conclusions about intervention effectiveness.
In literature reviews conflicting findings may lead to a conclusion that an intervention is ineffective or the research is uninterpretable.
Systematic reviews exploit divergent findings by examining potential explanations --- treatment differences, setting differences, etc. --- because conflicting outcomes may tell us where an intervention is likely to succeed or fail.
Systematic reviews use numeric and narrative information fully:
•a small effect across several studies may be significant
•program characteristics can be used to explain the effect.
Literature reviews are an inefficient way to extract program & outcome information, particularly if the number of studies is large, e.g.>30.
•It is impossible to mentally juggle relationships among so many variables.
Systematic Reviews
Another approach to the literature is systematic reviews.
A systematic review takes in account:
•the precise purpose of the review
i.e. stating a research hypothesis
•how studies are selected & included
Systematic reviews can answer:
•is there publication bias?
•are intervention programs similar enough to combine?
•what is the distribution of study outcomes?
Systematic review can answer:
•are outcomes related to research design?
•are outcomes related to characteristics of programs, participants, and setting?
•what are the needs for future research?
Purpose of the Guide to Community Preventive Services: systematic reviews & evidence-based recommendations
Are we building on a foundation of existing knowledge?
Explosive growth of scientific information
• too much to keep up with
• contradictory results
Increasing public doubt about scientific findings
Systematic reviews for research synthesis
• combine many studies with different methods and results
• look for consistencies in set of findings
• more robust than single study
• may pinpoint why studies differ
• shows what is effective and why
What counts as evidence?
Type 1 Type 2
Determinants or
associations between
risk and an outcome
Relative
effectiveness of
different interventions
“Something should
be done”
“This should
be done”
The Guide to Community Preventive Services
What strategies, targeted to which groups will:
•promote healthy choices?
•prevent disease and injury?
•improve environmental conditions to promote health?
Community Guide Topics
Environmental Influences• Sociocultural Environment
• Physical Environment
Risk Behaviors Specific Conditions• Tobacco Use• Alcohol Abuse/Misuse• Other Substance Abuse• Poor Nutrition• Inadequate Physical Activity• Unhealthy Sexual Behaviors
• Vaccine Preventable Disease• Pregnancy Outcomes• Violence• Motor Vehicle Injuries• Depression• Cancer• Diabetes• Oral Health
Central Questions
• program effectiveness
• feasibility of implementation
• acceptability to the population
• unanticipated harms (or benefits)
• cost-effectiveness
Steps to Conducting a Review
• Assemble a review team• Develop conceptual framework• Prioritize review topics• Define specific intervention for review• Search for and retrieve evidence• Rate quality of evidence• Summarize evidence• Translate into a recommendation
Assemble a Review Team
• Multiple perspectives and backgrounds – Improve completeness and accuracy of information – Reduce impact of individual/institutional
perspectives– Enhance usefulness of products
Develop Conceptual Approachto the Topic
• The Logic Model
LOGIC FRAMEWORK ILLUSTRATING CONCEPTUAL APPROACH TO NUTRITION & COMMUNITY HEALTH
Interventions Modifiable Determinants
Food Supply Factors -Agriculture policy
-Nutrition policy-Science and technology
-Food production, processing, storage and distribution
-Food fortification-Food safety
Environmental Factors
Availability & Price-Neighborhoods
-Schools-Worksites
-Homes-State and National
-Food and nutrition
assistance programs
Consumer Demand-Household resources
-Nutrition knowledge
-Cultural practices
-Psychosocial characteristics
-Taste and preferences
-Advertising and marketing
POPULATION FOOD INTAKE
Food Consumption Patterns (e.g. fruits, vegetables)
Intake of Nutrients and Food Components
VitaminsMinerals
FiberFats
Other food constituentsDietary supplements
AlcoholEnergy balance
Life StageRequirements
Pregnancy Lactation Childhood
Adolescence Adulthood
Older Adulthood
Intermediate Outcomes
Community Health
OutcomesPhysiologic Indicators
Growth
Adipose tissueMusculoskeletalGastrointestinal
MetabolicCardiovascularReproductiveImmunologicalNeurological
Genetics,Co-morbidities
Morbidity
Mortality
Measures ofHealth & Fitness
PhysicalActivityPatterns
Prioritize Intervention Topics
• Preventable disease burden
• Common practices that are questionable
• New approaches that are promising
• Topic of keen public health interest
Priority Ranked List of Topics
1. Food & beverage availability and price in schools.
2. Comprehensive community approaches to increase fruity & vegetable intake.
3. Food and beverage advertising to children.
4. Food & beverage availability, price, portion size, and labeling in restaurants.
5. Tax on sodas and snack foods.
6. Farm subsidies and production of fruits, vegetables, & whole grains.
7. Food choice and nutrition education in food assistance programs.
8. Nutrition and weight management counseling in healthcare settings.
9. Breast-feeding.
10 Product labeling in grocery stores, restaurants and vending machines.
11. Food & beverage availability and price in worksites.
12. Use of dietary supplements across the lifespan.
Specify the Review Question
• What population?
• What interventions or risk factors?
• What comparisons?
• What outcomes?
Example Question Do multi-component, school-based nutrition interventions
which may include:
– curricula (nutrition & physical activity)– food availability, accessibility, price– policy and environmental changes
improve nutritional behavior and nutritional status of children and adolescents in developed countries?
Environmentalsupport for healthy
choices
Nutrition & healthmessages
Promotion ofself-awareness,
self-efficacy
Multi-component
School-based
NutritionIntervention
s
Physiologic Indicatorsbody size &compositiongrowthfitnessHealth statusblood pressurecholesterolSchoolAchievementattendanceparticipationperformance
School Policy
Behaviors dietary intake physical activity
Knowledge nutritional needs food content
Attitudes self-care body image
Abilities self-assessment behavioral change skills media literacy
Analytic Framework
Inclusion Criteria
• Characteristics derived from the focused question
• Additional characteristics– Methodological– Publication dates– Languages– Relevant outcomes
Find Information
Select strategies for finding studies: – Database searches– Reviews of reference lists– Gray literature– Consultation with experts
Assess Quality
• Suitability of study design
•see handout
• Quality of study execution
•see handout
Suitability of Study Design
• Greatest– Prospective and – Concurrent comparison
• Moderate– Retrospective or– Multiple measurements over time; no
concurrent comparison
• Least– Single before and after measurement; no
concurrent comparison
Strength of Study Execution
• Description– Population– Intervention
• Sampling
• Measurement – Exposure– Outcome
• Analysis
• Interpretation of results
• Other
Exclude Studies Below Some Quality Threshold
• Exclude studies with limited execution (i.e., with many important threats to validity)
• Sometimes exclude studies with least or moderate suitability of design
Research Synthesis for Public Health Policy & Practice Decisions:
Systematic review of United States studies of .08 blood alcohol concentration laws
Lowering legal blood alcoholconcentration (BAC) limits
•Alcohol-related crashes cause 16,000 deaths and 300,000 injuries each year in the US
•Laws that lower BAC from 0.10 to 0.08 existed in less that half of US states
Analytic Framework:Lower Blood Alcohol Concentration Laws
LowerB.A.C.Laws Alcohol-
relatedcrashes
Drinking &driving
behaviors
PerceivedRisk ofArrest
Social normsregarding
drinking anddriving
Fatal &non-fatalinjuries
OUTCOME
Evidence base for .06 BAC Laws
Searched journal articles, technical reports and conference proceedings.
Nine studies were identified evaluated state BAC laws– all of sufficient design and quality.
All studies reported data from police incident reports of crashes on public roadways.
Evidence base for .06 BAC Laws
Eight of the nine studies reported percent change in alcohol-related fatalities (post-law period vs. pre-law period.
Other outcome data included public knowledge and perception of impaired driving laws, self-report of impaired driving, impaired driving arrests.
–50 -40 -30 -20 -10 0 10 20 30
Percent Change
Median percent change: -7% Interquartile range: -15%, -4%
States 15 States (1)* VA (2) VT (3,4,5) UT (5,3,4) OR (4,5,3) NC (6,2) NM(2) NH (2) ME(4,5,3) KS (2) FL (2) CA (5,7,8,3,4)
Percent Change in Measures of Alcohol -Related Motor Vehicle Fatalities, by State
Median percent change: -7%
Passed .08 BAC law in 2002
Passed .08 BAC law before the new national standard
States with .08 BAC Laws, 2002
Passed .08 BAC law in 2001
Who Is the Audience?
•Public health departments
•Health care systems
•Purchasers of health care
•Government and foundations
•Community organizations
Lack of Persuasive Evidence
• Lack of evidence does not mean that interventions don’t work
• Insufficient evidence may point to a
research agenda
Issues of Evidence
• We don’t have evidence about everything
• Enormous amount of evidence yet to review
• New evidence may change recommendations
• Capturing complexity
• Urgent needs and limited resources
• Participatory research
Translating Scientific Knowledge into Action
Task ForceRecommendations
andDissemination
Knowledge for InformedDecisions
Change in environments& behaviors
Program & policy
selection
Community Health
Outcomes
Implementation:• standards & protocols• program planning• funding decisions• policies & laws• research investments
www.TheCommunityGuide.org