Methodological Issues in Systematic Review Formulating Questions

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Methodological Issues in Systematic Review-
Formulating Questions -

• Joseph Lau, MD
• Tufts Medical Center EPC
• AHRQ Annual Meeting
• September 10, 2008

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Analytic framework for omega-3 FA intake and CVD
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Specific Key Questions

• What is the efficacy or association of omega-3
  fatty acids (DHA, EPA or ALA supplements, and
  fish consumption) in reducing CVD events
  (including all-cause mortality, CVD mortality,
  non-fatal CVD events, and new diagnosis of CVD)?
  In patients without known CVD (primary
  prevention) and with known CVD (secondary
  prevention).

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Specific Key Questions

• 2. Relative effects of omega-3 fatty acid
  sources, with specific emphasis on compositions,
  dosages, the ratio of omega-6 to omega-3 fatty
  acids, and potential interactions due to duration
  of intervention or exposure.
• What adverse events related to omega-3 fatty acid
  dietary supplements are reported in studies?

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Participants

• Primary Prevention - patients without prior
  history of cardiovascular disease
• Country
• Background diet
• Secondary Prevention patients with prior
  history of cardiovascular disease

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Interventions

• Fish
• Different kinds, preparation, amount, how intake
  was estimated
• Fish oil supplements
• Eicosapentaenoic acid (EPA) / Docosahexaenoic
  acid (DHA)
• a-linolenic acid ALA (walnut, canola oil, flax
  seed, etc.)

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Outcomes (endpoints)

• Clinical outcomes (events)
• Overall mortality
• Stroke
• Myocardial infarction
• Sudden death
• revascularization
• Surrogate/intermediate outcomes (biomarkers,
  measurements)
• Blood pressure
• Lipid levels

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The PICO method to formulate research question on
interventions
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Study design

• RCT
• Cohort
• Case-control
• Cross-sectional
• Other criteria
• Study size
• Year, language, etc

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Additional inclusion criteria

• Published English language literature
• Experimental or observational studies
• Reported original CVD outcome data and evaluated
  any potential source of omega-3 fatty acids
• At least 5 human subjects
• At least 1-year duration

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Issues in formulating a question

• Narrow versus broad (for individual or
  population)
• Clinically meaningful and useful (based on sound
  biological and epidemiological principles)
• Very broadly defined questions may be criticized
  for mixing apples and oranges
• Very narrowly focused questions may have no data
  or have limited generalizability and sometimes
  may lead to misinterpretations