The Functionality Assessment Flowchart (FAF): a new simple and reliable method to measure performance status with a high percentage of agreement between observers

BACKGROUND: Performance status (PS) assessment is an integral part of the decision-making process in cancer care. Karnofsky Performance Status (KPS) and Eastern Cooperative Oncology Group (ECOG) PS are the most widely used tools. In some studies, the absolute agreement rate of these tools between observers has been moderate to low. The present study aimed to evaluate the inter-observer reliability and construct validity of the new Functionality Assessment Flowchart (FAF) and compare it with ECOG PS and KPS in a sample of cancer patients. METHODS: The patients were recruited by convenience from the waiting rooms of the Breast and Gynecology Ambulatory in a cross-sectional study. Two trained medical students (observer A) and five medical oncologists (observers B) independently rated women according to the ECOG PS, KPS and FAF. After the determining the PS scores, observer A administered the Functional Assessment of Cancer Therapy-Fatigue (FACT-F) questionnaire to the participants. The agreements between observers A and B were investigated using the absolute agreement rate (%), weighted and unweighted kappa and Spearman’s correlation test. For construct validity, the PS scores were correlated with functional and fatigue scores by performing correlation analysis. RESULTS: Eighty women with a median age of 57 years were included in the study (86 % accrual rate). Among these women, 39 (48.8 %) had advanced cancer. The overall absolute agreement rate between observers was 49.4 % for KPS, 67 % for ECOG PS, and 78.2 % for FAF. When using unweighted kappa values, the inter-observer reliability was “fair”, “moderate” and “substantial” for KPS, ECOG PS and FAF, respectively. However, when using weighted kappa statistics, “substantial” agreement was observed for KPS and ECOG PS and “nearly perfect” agreement was observed for FAF. All of the PS scales correlated very well with the functional and fatigue scores. CONCLUSIONS: We present a new instrument with moderate to high inter-observer agreement and adequate construct validity to measure PS in cancer patients. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12885-015-1526-0) contains supplementary material, which is available to authorized users.