STROBE Statement

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• STROBE Statement
• STrengthening the Reporting of OBservational
  Studies in Epidemiology
• Iveta Simera
• The EQUATOR Network
• Centre for Statistics in Medicine, Oxford, UK
• April 2012

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Observational studies

• Many types of studies - right research design
  depends on the question we ask
• Observational studies
• Large proportion of research
• Can be valuable (e.g. AE) but also many
  disadvantages (confounding, bias)
• Without comparison group descriptive
• (do not try to qualify the relationships but give
  us a perspective of what is happening in the
  population, prevalence or experience of a group)
• Case reports, case series, qualitative studies,
  some cross-sectional studies (surveys)
• With comparison group - analytical
• (attempts to qualify relationship between two
  factors effect of an intervention / exposure on
  an outcome)
• Cohort studies, case-control studies, some
  cross-sectional studies

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Difference in analytical designs

• Experimental studies
• Researcher manipulates exposure by allocating
  participants to Intervention (Exposure) group

• Observational studies with a comparison group
• Researcher simply measures the exposure or
  treatments of the groups
• These studies all include matched groups of
  participants
• They assess associations between exposures and
  outcomes

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Cohort studies

• Cohort group of Roman soldiers
• Start with exposure (variable) then follow for
  outcome
• Data are obtained from groups who have been
  exposed or not exposed to the factor of interest
• Best for study the effect of predictive risk
  factors on an outcome

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Case-control studies

• Patients with a certain outcome or disease and an
  appropriate group of controls without the outcome
  or disease are selected
• (usually with careful consideration of choice
  of controls, matching)
• Information is obtained on whether the
  participants have been exposed to the factor
  under investigation

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Cross-sectional studies

• Examine the relationship between diseases (or
  other health-related characteristics) and other
  variable of interest as they exist in a defined
  population at one particular time
• (outcomes and exposures are both measured at
  the same time)
• Best for quantifying the prevalence of a disease
  or risk factor, and for quantifying the accuracy
  of a diagnostic test

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STROBE
Grimes, DA, Schulz KF. An overview of clinical
research the lay of the land. Lancet 2002 359
57-61.
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STROBE Statement

• Guidance on how to report observational studies
  well (which is rare!)
• Focus on 3 main study designs cohort,
  case-control, cross-sectional studies
• Published in Oct 2007 short paper and EE
• Adopted by many journals
• Find it on
• www.equator-network.org
• www.strobe-statement.org

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Three STROBE extensions (1)

• STREGA (2009)
• reporting of genetic association studies

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Three STROBE extensions (2)

• STROBE ME (Oct 2011)
• Reporting molecular epidemiology (biomarker
  studies)

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Three STROBE extensions (3)

• STROBE abstract
• - Reporting observational
• studies in conference
• abstracts (online draft)

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STROBE

• Checklist with 22 items
• Heading (where in paper), item No
• Recommendation, divided into cohort,
  case-control, cross-sectional study - where
  different

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• Title and abstract
• a) Indicate the studys design with a commonly
  used term in the title or the abstract
• b) Provide in the abstract an informative and
  balanced summary of what was done and what
  was found
• Introduction
• Background/Rationale
• Explain the scientific background and rationale
  for the investigation being reported
• Objectives
• 3. State specific objectives, including any
  prespecified hypothesis

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• Methods
• Study Design
• Present key elements of study design early in the
  paper
• (what design, what was compared, which controls
  and why...etc)
• Setting
• 5. Describe the setting, locations, and relevant
  dates, including periods of recruitment,
  exposure, follow-up, and data collection

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• Methods - continued
• Participants
• 6.a) Cohort study
• eligibility criteria
• sources and methods of participant selection
• follow-up methods
• Case-control study
• eligibility criteria
• sources and methods of case ascertainment and
  control selection
• rationale for the choices of cases and controls
• Cross-sectional study
• eligibility criteria
• sources and methods of participant selection

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• Methods - continued
• Participants
• 6.b) Cohort study
• For matched studies, give matching criteria and
  number of exposed and unexposed
• Case-control
• For matched studies, give matching criteria and
  the number of controls per case
• Variables
• 7. Clearly define all outcomes, exposures,
  predictors, potential confounders, and effect
  modifiers. Give diagnostic criteria, if
  applicable

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• Methods - continued
• Data sources/measurement
• 8. For each variable of interest, give sources
  of data and details of methods of assessment
  (measurement)
• Describe comparability of assessment methods
  if there is more than one group
• Give information separately for cases and
  controls in case-control studies and, if
  applicable, for exposed and unexposed in
  cohort and cross-sectional studies

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• Methods - continued
• Bias
• 9. Describe any efforts to address potential
  sources of bias
• (ie systematic deviation of a result from the
  true value)
• e.g. recall bias, detection bias,
  interviewer bias, selection bias

Very important in observational studies!
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• Methods - continued
• Study size
• 10. Explain how the study size was arrived at
• (should be large enough to arrive at a point
  estimate with a reasonably narrow confidence
  interval)
• Quantitative variables
• 11. Explain how quantitative variables were
  handled in the analyses. If applicable,
  describe which groupings were chosen and why

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• Methods - continued
• Statistical methods
• a) Describe all statistical methods, including
  those used to control confounding
• (?bias, confounding association true but
  caused by something else)
• b) Describe any methods used to examine
  subgroups and interactions
• c) Explain how missing data were addressed

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• Methods - continued
• Statistical methods - continued
• 12.d) Cohort study
• If applicable, explain how loss to follow-up
  was addressed
• Case-control
• If applicable, explain how matching of cases
  and controls was addressed
• Cross-sectional If applicable, describe
  analytical methods including sampling strategy
• e) Describe any sensitivity analyses

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• Results
• Participants
• 13. a) Report numbers of individuals at each
  stage of study - e.g., numbers potentially
  eligible, examined for eligibility, confirmed
  eligible, included in the study, completing
  follow-up, and analysed
• b) Give reasons for non-participation at each
  stage
• c) Consider use of a flow diagram
• Give information separately for cases and
  controls in case-control studies and, if
  applicable, for exposed and unexposed in cohort
  and cross-sectional studies

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• Results - continued
• Descriptive data
• 14. a) Give characteristics of study
  participants (e.g. demographic, clinical,
  social) and information on exposures and
  potential confounders
• b) Indicate number of participants with
  missing data for each variable of interest
• c) Cohort study
• Summarise follow up time (e.g. average and
  total amount)
• Give information separately for cases and
  controls in case-control studies and, if
  applicable, for exposed and unexposed in cohort
  and cross-sectional studies

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• Results - continued
• Outcome data
• 15. Cohort study Report numbers of outcome
  events or summary measures over time
• Case-control Report numbers in each
  exposure category, or summary measures of
  exposure
• Cross-sectional Report number of outcome
  events or summary measures
• Give information separately for cases and
  controls in case-control studies and, if
  applicable, for exposed and unexposed in cohort
  and cross-sectional studies

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• Results - continued
• Main results
• a) Give unadjusted estimates and, if applicable,
  confounder-adjusted estimates and their
  precision (e.g. 95CI). Make clear which
  confounders were adjusted for and why they were
  included
• b) Report category boundaries when continuous
  variables were categorised
• c) If relevant, consider translating estimates
  of relative risk into absolute risk for a
  meaningful time period

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• Results - continued
• Other analyses
• 17. Report other analyses done, e.g. analyses
  of subgroups and interactions, and sensitivity
  analyses
• Discussion
• Key results
• 18. Summarize key results with reference to
  study objectives
• Limitations
• 19. Discuss limitations of the study, taking
  into account sources of potential bias or
  imprecision. Discuss both direction and
  magnitude of any potential bias

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• Discussion - continued
• Interpretation
• 20. Give a cautious overall interpretation of
  results considering objectives, limitations,
  multiplicity of analyses, results from similar
  studies, and other relevant evidence
• Generalisability
• 21. Discuss the generalisability (external
  validity) of the study results

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• Other information
• Funding
• 22. Give the source of funding and the role of
  the funders for the present study and, if
  applicable, for the original study on which the
  present article is based
• More detailed explanation
• Vandenbroucke JP, von Elm E, Altman DA, et al.
  Strengthening the Reporting of Observational
  Studies in Epidemiology (STROBE) Explanation and
  Elaboration. PLoS Med 4(10) e297.doi10.1371/jour
  nal.pmed.0040297

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• www.equator-network.org
• www.strobe-statement.org