data.table containing the log-likelihoods for all event types,
and for the null hypothesis of no event, calculates the log-likelihood ratios
by subtracting null log-likelihoods from the event log-likelihoods,
for each location, stream, and event duration.
The identifier for the null hypothesis in the column
data.table with key columns
location, event, stream,
duration, and a column
llr containing the log-likelihood ratios for
each event type.