HistCite does not currently have the capacity to analyse subsets of data within a collection. At present you need to create a marked list of the records you want, export them as a set and then perform an analysis of the new set. A future version of HistCite will have subset analysis capability.
We are working on a statistical module which will include h-index and other popular bibliometrics.
(1) too bad that subsets are not possible. this makes some analysis very cumbersome. especially when looking into groupings and subgroups, or the time record of individuals / groups