No / We present a series of iterative methods to examine the problems associated with summed probability functions (SPFs) based on archaeological radiocarbon data. As a case study we use an SPF generated from a substantial radiocarbon data-set from the Irish Later Bronze and Iron Ages. We use simple numerical methods to show that real patterns can be deciphered from SPFs that can be used to trace and evaluate patterns of change. However, our results suggest that SPFs should not be used as a simple index of past human activity. / This research forms part of the project ‘Mobility, Climate and Culture: Re-modelling the Irish Iron Age’, funded by the British Academy through their BARDA scheme. Preliminary data collection was conducted as part of a pilot project funded by the Heritage Council of Ireland.