Charles L. Webber, Jr., Ph.D.

Professor Emeritus
Department of Cell and Molecular Physiology
Stritch School of Medicine
Loyola University Chicago
Health Sciences Division
2160 South First Avenue
Maywood, IL 60153 USA

RECURRENCE QUANTIFICATION ANALYSIS (RQA) is a powerful analytical tool developed over the last decade for the study of nonlinear dynamical systems. RQA is the necessary extension of recurrence plot analysis (RPA), a more qualitative tool. Since RQA methodology is independent of limiting constraints such as data set size, data stationarity, and assumptions regarding statistical distributions of data, RQA seems ideally suited for physiological systems characterized by non-homeostatic transients, state changes, and noise from within and without the organism or process. Mathematical details and the physiological utility of RQA are described in numerous papers with Joseph P. Zbilut, Ph.D., DNSc of Rush University (deceased Jan. 10, 2009).

RECURRENCE PLOTS AND QUANTIFICATION OF RECURRENCES are illustrated below for data derived from a normal human electrocardiogram (continuous flow). The input data for each plot consist of the same 480 consecutive RR intervals (discrete map) embedded in 5 dimensions. A local recurrence plot (left) is generated by keeping the radius low (15% of maxdist), allowing recurrences to occur only in near neighborhoods. A global recurrence plot (right) is generated by saturating the radius (100% of maxdist), allowing for all possible recurrences. The various colors reflect different Euclidean distances between trajectories and are analogous to geographical relief maps. Five RQA variables are computed (%recurrence, %determinism, information entropy, maximum diagonal line length, state trend) which have relevancy as nonlinear markers of changes in dynamical systems and physiological states. For specific details regarding RQA implementation (easy) and RQA interpretation (difficult), see our publications (above) and free software release (below).



RQA SOFTWARE that generates images like those above and other RQA utilities are embedded within downloadable ZIP file Download RQA161. The current distribution version of this software includes 57 executable RQA programs, 11 utility programs, 21 example data files, and an explanatory readme file READ2021.PDF and key monograph RQA_NLD.PDF.

Please contact Dr. Webber directly (phone, electronic mail, snail mail) with any questions regarding research applications of these RQA programs.

Created: August 22, 1996
Revised: August 12, 2021

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P: (708) 638-7497