From GameWatcher: “Call of Cthulhu is out now, and while it has some problems it’s still a worthy adventure-RPG to try. It has many stats that can affect puzzles and decisions, but one of the stats you can’t directly upgrade is Occultism. So how do you upgrade your Call of Cthulhu Occultism skill?”
Source: N4G PC Call of Cthulhu Occultism – How to Upgrade Occultism Skill