  We define a framework for determining constraints on the detection rate of
fast transient events from a population of underlying sources, with a view to
incorporating beam shape, frequency effects, scattering effects, and detection
efficiency into the metric. We then demonstrate a method for combining
independent datasets into a single event rate constraint diagram, using a
probabilistic approach to the limits on parameter space. We apply this new
framework to present the latest results from the V-FASTR experiment, a
commensal fast transients search using the Very Long Baseline Array (VLBA). In
the 20 cm band, V-FASTR now has the ability to probe the regions of parameter
space of importance for the observed Lorimer and Keane fast radio transient
candidates, by combining the information from observations with differing
bandwidths, and properly accounting for the source dispersion measure, VLBA
antenna beam shape, experiment time sampling, and stochastic nature of events.
We then apply the framework to combine the results of the V-FASTR and ATA Fly's
Eye experiments, demonstrating their complementarity. Expectations for fast
transients experiments for the SKA Phase I dish array are then computed, and
the impact of large differential bandwidths is discussed.
