Using Dynamically Defined Controls to Evaluate the Impact of an Ionization Technology

An additional field trial of an ionisation technology, called Atlant, was conducted in late 2010. Previous analysis of the data collected in field trials of the technology conducted in 2008 and 2009 used spatio-temporal statistical models to account for the impact of meteorological and topographic conditions not controllable by the randomised experimental design. In addition, a novel application of a random effect block bootstrap was developed for inference. These techniques are applied to the analysis of the 2010 Atlant field trial. In response to peer-review of previous trials, a new modelling approach is developed for this 2010 analysis, that uses dynamically defined upwind control areas to generate values of an instrumental variable that integrates the effects of meteorology and topography induced variation in rainfall. This allows a much simpler model specification and a clearer delineation between naturally occurring rainfall and any additional rainfall attributable to the operation of Atlant. Results using both the statistical methodology of previous trials and also by fitting this so-called “instrumental” model are consistent with those obtained in previous analyses, which had suggested a positive increases in rainfall of around nine percent relative to the predicted rainfall that would have occurred in the absence of Atlant operation.