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01.12.2013 | Study protocol | Ausgabe 1/2013 Open Access

BMC Medical Research Methodology 1/2013

Protocol for a systematic review and individual patient data meta-analysis of prognostic factors of foot ulceration in people with diabetes: the international research collaboration for the prediction of diabetic foot ulcerations (PODUS)

BMC Medical Research Methodology > Ausgabe 1/2013
Fay Crawford, Chantelle Anandan, Francesca M Chappell, Gordon D Murray, Jacqueline F Price, Aziz Sheikh, Colin R Simpson, Martin Maxwell, Gerard P Stansby, Matthew J Young, Caroline A Abbott, Andrew JM Boulton, Edward J Boyko, Thomas Kastenbauer, Graham P Leese, Matteo Monami, Matilde Monteiro-Soares, Stephen J Rith-Najarian, Aristidis Veves, Nikki Coates, William J Jeffcoate, Nicola Leech, Tom Fahey, Jayne Tierney
Wichtige Hinweise

Electronic supplementary material

The online version of this article (doi:10.​1186/​1471-2288-13-22) contains supplementary material, which is available to authorized users.

Competing interests

The authors have no financial competing interests.

Authors’ contributions

FC is the Chief Investigator, and GDM the Principal Investigator with overall responsibility for the statistical analysis, together with CA and FMC they form the Data Management Committee and have day to day responsibility for the research. Together with JFP, AS,CRS, GPS,MJY and MM they form the research steering committee each of whom are co-investigators and have contributed to the design and writing of the research protocol. CAA,AJMB,EJB,TK,GPL,MM,MM-S,SJR-N,AV are the principal investigators/corresponding authors on all cohort studies identified by the review search strategy. They have contributed individual patient data to the meta analysis. Together with the Research Steering Committee and the independent advisors they form the international steering committee work closely with members of the data management committee in the preparation of the data. NC,WJJ,NL,TF,JT are the project independent advisors who make clinical and methodological contributions. They have collaborators status and are members of the International Steering committee. All authors read approved the final manuscript.



Diabetes–related lower limb amputations are associated with considerable morbidity and mortality and are usually preceded by foot ulceration. The available systematic reviews of aggregate data are compromised because the primary studies report both adjusted and unadjusted estimates. As adjusted meta-analyses of aggregate data can be challenging, the best way to standardise the analytical approach is to conduct a meta-analysis based on individual patient data (IPD).
There are however many challenges and fundamental methodological omissions are common; protocols are rare and the assessment of the risk of bias arising from the conduct of individual studies is frequently not performed, largely because of the absence of widely agreed criteria for assessing the risk of bias in this type of review. In this protocol we propose key methodological approaches to underpin our IPD systematic review of prognostic factors of foot ulceration in diabetes.
Review questions;
1. What are the most highly prognostic factors for foot ulceration (i.e. symptoms, signs, diagnostic tests) in people with diabetes?
2. Can the data from each study be adjusted for a consistent set of adjustment factors?
3. Does the model accuracy change when patient populations are stratified according to demographic and/or clinical characteristics?


MEDLINE and EMBASE databases from their inception until early 2012 were searched and the corresponding authors of all eligible primary studies invited to contribute their raw data. We developed relevant quality assurance items likely to identify occasions when study validity may have been compromised from several sources. A confidentiality agreement, arrangements for communication and reporting as well as ethical and governance considerations are explained.
We have agreement from the corresponding authors of all studies which meet the eligibility criteria and they collectively possess data from more than 17000 patients. We propose, as a provisional analysis plan, to use a multi-level mixed model, using “study” as one of the levels. Such a model can also allow for the within-patient clustering that occurs if a patient contributes data from both feet, although to aid interpretation, we prefer to use patients rather than feet as the unit of analysis. We intend to only attempt this analysis if the results of the investigation of heterogeneity do not rule it out and the model diagnostics are acceptable.


This review is central to the development of a global evidence-based strategy for the risk assessment of the foot in patients with diabetes, ensuring future recommendations are valid and can reliably inform international clinical guidelines.
Additional file 1: Appendix 1: Flow diagram of the stages in an IPD review adapted from Stewart and Clark 199510. (DOC 125 KB)
Additional file 2: Appendix 2: Embase and MEDLINE searches. (DOC 54 KB)
Additional file 3: Appendix 3: Questionnaire to determine the methodological standards adopted in cohort studies evaluating the prognostic factors for foot ulceration in diabetes. (DOC 67 KB)
Additional file 4: Appendix 4: List of the most common variables reported in cohort studies. (DOC 62 KB)
Additional file 5: Appendix 5: Committees and members. (DOC 57 KB)
Additional file 6: Appendix 6: Data agreement for the collaborators. (DOC 68 KB)
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