Compute
the Information Component credibility interval, typically the lower end of
the 95% CI, also known as the IC025.
Details
The ends of the credibility interval of the information component
are estimated with the gamma distribution.
n_exp is defined as n_drug * n_event / n_total for the basic IC
(formula is different for interactions)
Do not add +.5 to n_obs and n_exp as it is automatically done in the function.
By default, IC025 is computed. Change p for different ends.
It may be easier to use compute_dispro(), which internally calls this function.
