Systematic Reviews Michael Chaiton Tobacco and Health: From Cells to Society September 24, 2014

Outline Science and the pursuit of truth A history of the systematic review in tobacco Conducting a systematic review Your assignment

Truth with a capital “T”

Causation Every cause is just a slippery story, a catchy conjecture, a lively conception produced by habit

Koch’s Postulates Specificity – In diseased organisms, not in healthy Isolatable – Grow it in a culture Lead to disease – Cultured product in healthy organism Re-isolatable

Fisher’s Test: Randomization

Public Health Paradigm Ethical issues with randomization Pragmatic history

The Case-Control Study Compare characteristics of diseased patients to a group without the disease 1950’s studies of lung cancer and smoking

The Cohort Study Cuyler Hammond and others argued that case-control studies were explorative only Conducted ACS cohort study (1954)

Studies are not conclusive “Pure political rhetoric” Cohort studies were self-selected, not randomized

Definitive answers “The doctrine that one must never assess what has already been learned until the last possible piece of evidence is in would be a novel one for science.“ Call for Expert Panel Review of the Evidence

The Surgeon General Review the evidence according to objective criteria – Consistency – Strength – Specificity – Temporal relationship – Coherence

Process Defining the parameters Gathering all of the literature that answered the research question Summarizing the literature Critiquing the literature Conclusion

Systematic reviews Defined search strategy that aims to detect as much of the relevant literature as possible. Document their search strategy so that readers can assess its rigour and completeness. Explicit inclusion and exclusion criteria. Specify the information to be obtained from each primary study including quality criteria by which to evaluate each primary study. Prerequisite for quantitative meta-analysis, but not all systematic review are meta analyses

Types of reviews Traditional or narrative review Meta-Analysis Scoping Integrative Realist Rapid Review of reviews

Why a systematic review? Reduce bias Replicability Resolve controversy between conflicting studies Identify gaps in current research Provide reliable basis for decision making

Developing a Research Question Participants I(E)intervention (exposure) Comparison group Outcome(s)

Search Strategy Databases Manual search of key journal Review of references Search of personal files Consult with experts

Search Strategy Assess for relevance: – Inclusion/exclusion – Titles, abstracts, body Pilot strategy or use iterative process Lets others replicate or have confidence in your search (but not a lab book)

Synthesis Extract data Narrative Descriptive (Tables) Meta-analysis

What to include Sample size for each intervention Estimates effect size for each intervention with standard errors for each effect Difference between the intervention and control, and the confidence interval for the difference Units used for measuring the effect.

Assess for Quality Different rating systems exist Identify biases: – Selection bias—systematic difference in who is exposed – Performance bias—systematic difference to how the group are treated—researcher bias – Measurement bias—systematic differences in measurement – Attrition bias—systematic differences in who is around to have an outcome.

Critique Alternative explanation or potential heterogeneity Not necessarily quality

Conclusions Role of values: systematic reviews are not designed to make decisions, simply to assist in making them A single study is almost never conclusive

Close enough for public health

Your assignment Plan and conduct a systematic review on the topic of your choice Emphasize completeness of process over amount of content – I.e.., rigour counts more than scope – Keep scope manageable for you

Abstract An abstract of your research a)demonstrate the form of an abstract b)provide an outline for your research paper 300 words with the structure of an abstract – (intro, methods, results, conclusions, etc) – Focus on research question (PICO) and search strategy

Poster Design a poster in powerpoint – (clear layout, creativity) Expand on the outline—full findings. Refine question if necessary Critique quality Identify possible heterogeneity,

Debate A different way of summarizing evidence Exercise in making a persuasive case Assigned a position (pro or con) 5 minutes sharp