A weekend post on Slugger O'Toole about the year on year decline in the sales of the local NI daily newspapers sparked by curiosity, so I dug out* the longer term data and graphed it to show the performance (using the six monthly Audit Bureau of Circulation figures) of the Belfast Telegraph, Irish News and News Letter. I've added in the the Irish Times sales for comparison.
The overall trend is one of decline. However, it is significantly more pronounced for the Belfast Telegraph.
In fact if simple linear trend lines are added to the graph, sales of the Irish News and Belfast Telegraph will collide towards the end of 2012/beginning of 2013.
Statistically, a more sophisticated trend analysis would be required before drawing any formal conclusions. (Applying a polynomial trend line keeps clear water between the two publications for much longer.)
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* dug out is a euphemism for did a Google search to find different archive newspaper articles that quoted the six monthly figures as I only have access to the last set of stats on the ABC website!