Two-exponent Lavalette function. A generalization for the case of   adherents to a religious movement
  The Lavalette function is generalized to a 2-exponent function in order to represent data looking like a sigmoid on semi-log plots. A Mandelbrot trick is suggested for further investigations, if more fit parameters are needed. The analyzed data is that of the number of adherents to the main religions in the XXth century. 
Marcel Ausloos
physics.soc-ph