Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Correspondence
  • Published:

Observational studies and the chicken and egg issue in stroke

Nature Reviews Neurology volume 13, page 382 (2017)Cite this article

Subjects

Access through your institution
Buy or subscribe

In a News & Views article (Are care and outcomes better for participants of stroke trials? Nat. Rev. Neurol. 12, 498–499; 2016)1, Mary Joan Macleod and Carl E. Counsell commented on our recent publication2, in which patients with stroke who participated in research were found to receive better care and experience fewer in-hospital deaths than patients not participating in research. We thank Dr Macleod and Dr Counsell for their interest in our article, and for their comments, which highlighted the limitations of observational studies for exploring this topic. Overall, the important message was that research participants appear to have a greater likelihood of receiving care in stroke units. Therefore, are the observed benefits attributable to participation in research, or to the fact that being on a stroke unit — which in itself is known to improve outcomes — increases the opportunity to take part in research studies?

We agree that it was not possible for us to adjust for all potential confounders, as is often the case in nonrandomized studies. In particular, we were unable to adjust for the fact that patients who participate in research are often a prognostically more favourable group, as poor health and existing comorbidities generally preclude patients from participating in research with long-term follow-up. The likelihood of residual confounding was clearly stated in our discussion. Although the odds ratio for in-hospital death was large following adjustment for the available confounders, the imprecision of this result was apparent from the wide confidence intervals reported in our paper. This level of uncertainty guided our conservative conclusion that those who participate in research “potentially have improved in-hospital survival.”

This is a preview of subscription content, access via your institution

Access options

Access through your institution

Buy this article

  • Purchase on SpringerLink
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

References

  1. Macleod, M. J. & Counsell, C. E. Stroke: are care and outcomes better for participants of stroke trials? Nat. Rev. Neurol. 12, 498–499 (2016).

    Article  PubMed  Google Scholar 

  2. Purvis, T., Hill, K., Kilkenny, M., Andrew, N. & Cadilhac, D. Improved in-hospital outcomes and care for patients in stroke research: an observational study. Neurology 87, 206–213 (2016).

    Article  PubMed  PubMed Central  Google Scholar 

  3. Jovin, T. G. et al. Thrombectomy within 8 hours after symptom onset in ischemic stroke. N. Engl. J. Med. 372, 2296–2306 (2015).

    Article  CAS  PubMed  Google Scholar 

  4. Cadilhac, D. A., Pearce, D. C., Levi, C. R. & Donnan, G. A. Improvements in the quality of care and health outcomes with new stroke care units following implementation of a clinician-led, health-system redesign programme in New South Wales, Australia. Qual. Saf. Health Care 17, 329–333 (2008).

    Article  CAS  PubMed  Google Scholar 

  5. Stroke Unit Trialists' Collaboration. Organised inpatient (stroke unit) care for stroke. Cochrane Database Syst. Rev. 9, CD000197 (2013).

  6. National Stroke Foundation. National Stroke Audit Acute Services Report 2015. StrokeFoundation.au https://informme.org.au/-/media/A3039E82D9FF4BC7803B5C67B42DBBB0.ashx?la=en (2015).

Download references

Author information

Authors and Affiliations

  1. Tara Purvis and Dominique A. Cadilhac are at the Translational Public Health and Evaluation Division, Stroke and Ageing Research, School of Clinical Sciences at Monash Health, Monash University, Level 1/43-51 Kanooka Grove, Clayton, Victoria 3168, Australia.,

    Tara Purvis & Dominique A. Cadilhac

Authors
  1. Tara Purvis
    View author publications

    Search author on:PubMed Google Scholar

  2. Dominique A. Cadilhac
    View author publications

    Search author on:PubMed Google Scholar

Corresponding author

Correspondence to Tara Purvis.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

PowerPoint slides

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Purvis, T., Cadilhac, D. Observational studies and the chicken and egg issue in stroke. Nat Rev Neurol 13, 382 (2017). https://doi.org/10.1038/nrneurol.2017.59

Download citation

  • Published:

  • Issue date:

  • DOI: https://doi.org/10.1038/nrneurol.2017.59

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing