Unidimensional Fuzzy Pain Intensity Scale Ernesto Araujo, Member, IEEE, Susana Abe Miyahira Abstract— A fuzzy pain scale for representing subjectivity and emotionality related to the fifth vital sign of medical condition is proposed in this paper. The classic intensity rating scales are inherently crisp sets. The medical and healthcare community does not realize that since the concept of fuzzy sets does not range all fields of knowledge yet. This paper extends the accepted international classic pain intensity rating scales to fuzzy set theory obtaining the fuzzy visual analog scale (FVAS), fuzzy numerical rating scale (FNRS), fuzzy qualitative pain scale (FQPS), and fuzzy face pain scale (FFPS). These fuzzy pain intensity scales take into account positive characteristics concerning classic pain intensity scales meanwhile represent the inherent imprecision, uncertainty and vagueness presented in the pain report and assessment. The proposed approach demonstrates how fuzzy set theory may push forwards the boundaries of medicine and healthcare by proposing a novel approach in order to improve the human quality level. I. I NTRODUCTION Along with the four standards and well known vital signals of (i) Body Temperature, (ii) Pulse Rate, (iii) Blood Pressure, and (iv) Respiratory Rate, as traditionally assigned and monitored by medical and healthcare professionals, there has been still a fifth important measure in recent years. Pain has received the official assignment as the fifth vital sign for representing basic bodily functions and health quality of life [1], [2]. Since it is mostly a feature observed and reported by the patient, and usually not measured by using instruments during a physical examination, it is subjective, and not objective as expected from a medical sign. Even in the presence of controversy, if it is better understood as a symptom – i.e., noticed by a patient and not measured – more than a sign, pain has assumed a detached place in diagnosing medical conditions related to the presence of disease or abnormality. The importance of pain as a fundamental element for health care is recognized in [3], [4]. Moreover, in order to promote pain as the 5th vital sign and to offer guidelines for comprehensive pain assessment the regional Joint Commis- sion on Accreditation of Healthcare Organizations (JCAHO) Ernesto Araujo is with Integration and Testing Laboratory (LIT) and Space Engineering and Technology (ETE), at Instituto Nacional de Pesquisas Espaciais (INPE), Av. Astronautas, 1758, 12.227-010, S˜ ao Jos´ e dos Campos, SP, Brazil; with Health Informatics Department (DIS), at Universidade Federal de S˜ ao Paulo (UNIFESP), R. Botucatu, 862, 04023-062, S˜ ao Paulo, SP, Brazil; with the Hospital Municipal Dr. Jose de Carvalho Florence (HMJCF), Av. Saigiro Nakamura, 800, 04023-062, S˜ ao Jos´ e dos Campos, SP, Brazil; and Assoc. Paulista para o Desenvolvimento da Medicina (SPDM), R. Napoleo de Barros, 715, 04024-002, S˜ ao Paulo, SP, Brazil. (email: ernesto.araujo@{unifesp.br,lit.inpe.br}) Susana Miyahira is both with the Anesthesiology Dpt., Hospital Munic- ipal Dr. Jose de Carvalho Florence, Av. Saigiro Nakamura, 800, 04023- 062, S˜ ao Jose dos Campos, SP, Brazil and with Universidade Federal de S˜ ao Paulo (UNIFESP), R. Botucatu, 862, 04023-062, S˜ ao Paulo, SP, Brazil (email: susana miyahira@uol.com.br). officially recognized pain as a health problem, and in 2000 published a standard manual for driving medical and health care conducts [5]. Despite its importance, pain is often assumed to be difficult to grade or score due to its physiological, psychological, and cultural mechanisms bore by learned behavioral re- sponses related to individual life experience [6], [7]. Pain is considered as being an emotional, complex perceptual, subjective, and personal phenomenon involving all domains of an individual life experience. It is usually measured by employing unidimensional or multidimensional characteris- tics according to the objective and interests to be achieved during diagnosis. Further, even if the patient‘s pain would be reported by family members or friends, be classified ac- cording to patient’s behaviors, or indicated by physiological parameters, there is no standard approach that allows the objective, external observation. The patient’s self-report of pain is still considered the single, most reliable indicator of how much pain the patient is experiencing. Although the patient’s self-report is the preferable indi- cator of pain it is necessary a correct evaluation of pain manifestation. A common language to appropriately translate pain between the patient and the medical and healthcare professionals are pain measurement scales and methods that work as standard, or systematic mechanisms. Nevertheless, due to the subjectivity related to the pain fifth vital sign, there is no consensus on how to measure it and a myriad of pain measurement scales came up. The general indexes/scales of Brief Pain Inventory (BPI) [8], Descriptor differential scale (DDS) [9], Dolorimeter Pain Index (DPI) [10], McGill Pain Questionnaire (MPQ) [11], [12], [13], Numerical 11 point box Scale (BS-11) [14], Numeric Rating Scale (NRS-11) [15], Visual analog scale (VAS) [4], Walid-Robinson Pain Index (WRI) [16], as well as the specialized tests of Colorado Behavioral Numerical Pain Scale [17] for sedated patients, Pediatric Pain Questionnaire (PPQ) [18], Premature Infant Pain Profile (PIPP) [19], and Schmidt Sting Pain Index [20] or Starr sting pain scale [21] are, among others, the main pain measurement mechanisms employed during medical diagnosis. This paper addresses the subjectivity of the pain reported by patients by using fuzzy sets. The proposed approach is employed, but not limited, to deal with unidimensional scale. While the classical multidimensional scales are restrict to use in specific conditions due to their high complexity and diffi- culty of applicability and reproductively, the unidimensional scales are of immediate and general applications. Moreover, the JCAHO standard manual also reinforces the preference for using easier tools as the key element for successful pain assessment and treatment.