The problems of predicting and of pricing residential electricity consumption are closely related to the technical problem of the term of stability of pattern. Indeed, the general meaning of the word "pattern" would normally imply an assumption of stability, and here we attempt quantifying this notion: from being specific to some measurement data, to being characteristic of a household. Our working objective is to assess the stability of electricity consumption by selected Swedish households, and our main statistical instrument is a specially-devised coefficient of auto-similarity. Households are represented by sequences of readings of energy consumption, spaced at equal time intervals. (C) 2015 Published by Elsevier Ltd.