  How a household varies their regular usage of electricity is useful
information for organisations to allow accurate targeting of behaviour
modification initiatives with the aim of improving the overall efficiency of
the electricity network. The variability of regular activities in a household
is one possible indication of that household's willingness to accept incentives
to change their behaviour.
  An approach is presented for identifying a way of representing the
variability of a household's behaviour and developing an efficient way of
clustering the households, using these measures of variability, into a few,
usable groupings.
  To evaluate the effectiveness of the variability measures, a number of
cluster validity indexes are explored with regard to how the indexes vary with
the number of clusters, the number of attributes, and the quality of the
attributes. The Cluster Dispersion Indicator (CDI) and the Davies-Boulden
Indicator (DBI) are selected for future work developing various indicators of
household behaviour variability.
  The approach is tested using data from 180 UK households monitored for over a
year at a sampling interval of 5 minutes. Data is taken from the evening peak
electricity usage period of 4pm to 8pm.
