Since the seminal contribution of Case and Shiller (1989) several papers on the efficiency properties of housing markets have appeared. Nevertheless, there is still not full agreement on whether the housing market functions as an efficient market or not. In the present paper we apply two different methods, developed by Hjalmarsson and Hjalmarsson (2009), and Robertsen and Theisen (2011), along with a new data set. We examine whether methodological differences may explain the somewhat conflicting results of these authors. In order to focus on the role of the modes of analysis, we use data only for cooperative housing, and concentrate on one single issue, namely on whether variations in mutual debt between different dwellings is perfectly reflected in the price at which the dwellings are sold.