Interconversion of three measures of performance status: An empirical analysis
Introduction
Performance status represents a global assessment of a patient’s functional capacity, which reflects the additive physical, physiological and psychological effects of the disease process. In research settings, measures of performance status are used to assess eligibility and stratify patients for cancer clinical trials1 and to assess the predicted or actual efficacy of anti-cancer treatment. In clinical practice, performance status is used to estimate prognosis,2, 3, 4, 5 to predict toxicity and likelihood of response to therapy6 and to assess needs for services such as home care.7 Performance status assessments have also been incorporated into measures of quality of life.8, 9 Measures of performance status are generally completed by physicians, although inter-rater reliability among different disciplines is good.10, 11, 12, 13
The scales most commonly used in oncology for performance status assessment are the Karnofsky Performance Status (KPS) and the Eastern Cooperative Oncology Group (ECOG) scales (Fig. 1).14, 15 The KPS, developed in 1948,14 is an 11-point scale with scores ranging from 100 (normally active) to 0 (dead). The Eastern Cooperative Oncology Group (ECOG) scale was developed in 1960, and is a simpler 6-item scale that ranges from 0 (normal activity) to 5 (death).15 More recently, the Palliative Performance Scale (PPS) was developed, based on a modification of the KPS, to aid decision making and communication in palliative care settings.7 Similar to the KPS, it is an 11-point scale that includes assessment of ambulation, activity, extent of disease and self-care; in addition, oral intake and level of consciousness are also assessed (Fig. 1).
The reliability and validity of the KPS and PPS measures have been established in several studies,16, 17, 18, 19 as has the excellent intra- and inter-rater reliability of the KPS and ECOG scales among physicians.16, 20, 21 The PPS is increasingly regarded as the scale of choice in palliative care settings,22 while either the ECOG or the KPS scale is typically used in general oncology care. In order to improve communication among health care providers who use different measures, it is important to understand how scores on these measures correspond to each other.
Two prospective studies – both published more than a decade ago23, 24 – have assessed interconversion of the ECOG and the KPS measures. In one study, one physician conducted assessments on 150 patients attending a radiation therapy clinic.23 Using linear regression, point estimates and confidence intervals were derived; these showed a high level of error, especially in the lower ends of performance status. In the other, two physicians conducted assessments on 536 patients with lung cancer accrued over 6 years, which were evaluated using non-parametric statistics.24 More recently, investigators prospectively evaluated 75 patients with advanced non-small cell lung cancer with both ECOG and KPS; patients with ECOG 0–2 or KPS ⩾60 were eligible.25 Correlation of the two scales was fairly high (r = 0.75), but 21 patients with ECOG 2 were as likely to be rated as having KPS 60, 70 or 80. Conclusions from these studies are limited because they included small numbers of patients and/or only patients with lung cancer. No previous studies have examined systematically all possible KPS–ECOG combinations and none included the PPS measure.
The purpose of our study was to assess whether it was possible to construct an accurate conversion table to convert scores among the ECOG, PPS and KPS measures. Specifically, we hypothesised that there would be a high level of agreement between the PPS and the KPS measures, since the PPS was derived from the KPS.7 For the conversion between PPS or KPS and ECOG, we made no assumptions about which combination would have the best agreement. Rather we empirically tested all possibilities.
Section snippets
Study setting and procedures
The study was conducted at Princess Margaret Hospital, a comprehensive cancer centre which is a member of the University Health Network (UHN) in Toronto, Canada. Eligible patients were all those attending the Oncology Palliative Care Clinic (OPCC) or admitted to the Lederman Palliative Care Centre (PCC), a 12-bed acute palliative care unit. The study initially began in the OPCC; to increase the numbers of patients with poor performance status, the study was expanded to the PCC, concentrating on
Study population and patient characteristics
From April 1, 2007, to December 31, 2008, 3291 complete performance status assessments were made on 1385 patients. Out of 3291 performance evaluations, 3108 were measurements for outpatients and 183 were measurements for inpatients. The overall completion rate was 80% (82% for outpatients and 56% for inpatients). In order to reduce the cohort to a single measurement per patient, the assessment with the poorest performance status was selected per patient; in case of a tie in performance, the
Discussion
In this study, we have derived empirically a scale to convert scores among the ECOG, KPS and PPS scales using a large sample of patients with advanced cancer (Table 4). Although other studies have compared the ECOG and KPS,23, 24, 25 this is the first study to include the PPS, and the first to include a large number of patients with different tumour types. It is also the first study to assess KPS–ECOG performance scale equivalences by testing the level of agreement for all possible combinations
Conflict of interest statement
There were no conflicts of interest for any of the authors.
Acknowledgements
We extend our thanks to the clinical and research staff of the oncology palliative care clinic for their facilitation of this research. This research was funded in part by the Canadian Cancer Society (CCS, Grant #020509; CZ) and by the Ontario Ministry of Health and Long Term Care (OMOHLTC). The views expressed do not necessarily reflect those of the OMOHLTC. The funding agencies had no role in the study design, data collection, analysis and interpretation, writing or decision to submit for
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