A new method to determine a fractal dimension of nonstationary biological time-serial data

We devised a new analysis using quartile deviation of integrated and subtra cted fluctuation, termed QIS-A, to determine a fractal dimension of non-sta tionary fluctuation. In the algorithm, computations of the quartile deviati on, Q(n), of all integrated and subtracted fluctuations are repeated over a ll scales (n). The fractal scaling exponent is determined as a slope of the line relating log Q(n) to log n. Comparison of the QIS-A and a spectral an alysis using 20 computer-simulated fractional Brownian motions demonstrates robustness of the QIS-A to non-stationary fluctuations. (C) 2000 Elsevier Science Ltd. All rights reserved.