The scientific background about the methodology underlying the IMK business cycle indicator has been published in:

Proaño, C. R. und Theobald, T. (2014): Predicting Recessions with a Composite Real-Time Dynamic Probit Model. International Journal of Forecasting30(4), 898-917 

Since January 2012 the business cycle indicator has been updated monthly and published. Visit http://www.boeckler.de/imk_38710.htm  for further information  on the IMK Business Cycle Indicator.