Page 22 - Predicting survival in patients with spinal bone metastasesL

CHAPTER II
Eligibility criteria
Both prospective and retrospective studies were eligible for inclusion if they met the following criteria: (1) Sample size of at least 100 patients with spinal bone metastases from solid tumors (i.e. no hematological malignancies); (2) The study did not focus on one single primary malignancy; (3) Prognostic factors for survival were assessed by means of a multivariate analysis; (4) Studies were published in the English, German or Dutch language. If studies were derived from identical databases, the most comprehensive study was selected; separately published subgroup analyses were disregarded. Eligibility of studies was assessed by two independent review authors (W.J. and L.B.). A consensus meeting was planned to resolve disagreements. If disagreements persisted, a third review author (P.D.S.D.) was consulted.
Risk of bias
The risk of bias was assessed according to the guidelines provided by Hayden et al.14 In short, six main sources of potential bias (study participation, study attrition, prognostic factor measurement, outcome measurement, confounding and analysis) were assessed using a 29-item checklist. The six sources of bias were scored as being ‘high; 3 points’, ‘moderate; 2 points’, or ‘low; 1 point’. Therefore, the total number of points for each study ranged from 6-18, with a cut-off set at a maximum of 50% (≤9 points) for distinguishing a low risk of bias study from a high risk of bias study. Two review authors (W.J. and L.B.) independently scored the risk of bias for each study. A consensus meeting was planned to resolve disagreements. If disagreements persisted, a third review author (P.D.S.D.) decided on the risk of bias.
Data extraction
The data extracted from eligible studies consisted of the design, source of funding, setting, sample size, duration, inclusion and exclusion criteria, all prognostic factors investigated, duration of follow-up and results. If similar prognostic factors were investigated by different means, they were combined for the level of evidence analysis. For instance, the prognostic factor Performance status was assessed by means of the Karnofsky score15 or the Eastern Cooperative Oncology Group score.16 Other combined prognostic factors were Neurologic deficit; consisting of the Frankel score17 and ambulatory status, as well as the variable Primary tumor; consisting of several different sub classifications. Prognostic factors such as Age
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