Having recently obtained an old edition of RuneQuest (Runequest III to be specific), from which the Chaosium BRP system is ultimately derived, I discovered that this was not always the case. Runequest includes a complete system for modifying starting skills in the light of stats. I can only speculate about the reasons why this system was not carried over – perhaps because it adds to character creation time in a game where character mortality and hence re-creation is quite high, higher than the steadily improving heroes of RQ. The skill list in CoC is also longer, resulting in more book-keeping for your soon-to-die-horribly investigator. Still, DG agents have a slightly higher survivability than classic Investigators thanks to the modern combination of heavy weaponry, organisational backup, Prozac and Thorazine, so this caveat no longer necessarily applies. The following adopts the RQ III system to Call of Cthulhu 5.6.

• Skills are classed into six categories. Each category has a “modifier” score that is derived from the relevant stats. This modifier affects both the starting skill, and skill improvement (see below), so should be recorded.

• Each modifier has a primary stat associated with it, and may have one or more secondary or negative stats associated with it.

• If a stat is primary, then every point of the stat above 10 adds 1% to the modifier, and every point below 10 subtracts 1%.

• If a stat is secondary, then every two points of the stat above 10 adds 1% to the modifier, and every two points below 10 subtracts 1% - round down. No modifier can be changed by more than 10% by the secondary stats.

• If a stat is negative, then every point of the stat above 10 subtracts 1% from the modifier, and every point below 10 adds 1%.
  

Since EDU determines the basic number of skill points (and doesn’t appear in RQ), I have left it out to avoid double-dipping.

Categories:
Agility Skills:
DEX is primary. Dexterity = Agility.
STR is secondary. Being strong helps you move yourself around.
SIZ is negative. Being big and bulky can slow you down.
Skills: Climb, Dodge, Drive, Jump, Martial Arts, Ride, Swim, Throw, unarmed combat skills.

Communication Skills:
INT is primary. If you can’t think what you’re saying, you can’t say what you’re thinking.
POW is secondary. Charisma and that aura of authority make good listeners.
APP is secondary. If you’re good looking, you’ll draw favourable attention to your words.
Skills: Bargain, Credit Rating, Debate, Fast Talk, Persuade, Sing, Speak Own/Other Language.

Knowledge Skills:
INT is primary. Smart people know stuff gooder.
Skills: Knowledge based skills.

Physical Manipulation Skills:
DEX and INT are primary. You have to have the dexterity to manipulate the thing, and the brains to know what to do with it.
STR is secondary. Being strong helps hold things still/steady/in the right place/etc.
Skills: Conceal, Craft, Operate Heavy Machinery, Electrical Repair, Mechanical Repair, Locksmith, Pilot (thing), Firearms and armed combat skills.

Perception Skills:
INT is primary. If you aren’t smart enough to know where to look, you won’t look there.
POW and CON are secondary. POW gives you hunches and insight, while a high CON means sharp, healthy eyes and ears.
Skills: Listen, Psychology, Spot Hidden, Track

Stealth Skills:
DEX is primary. If you stumble, you’re noisy.
SIZ and POW are negative. A big person has more to hide, and a powerful magic aura won’t help you hide from a powerful magic monster.
Skills: Conceal, Disguise, Hide, Pick Pocket, Sneak

It can be seen that INT becomes a very powerful stat under this system. Keepers may wish to reduce the non-occupation specific skill points allocated in character creation from INT * 10 to INT * 8 or so to compensate.

These modifiers also affect one’s chances of advancing in a skill. They are added (or subtracted) to the roll for a relevant skill check (when one attempts to roll above one’s skill). As a result, it is possible for skills to go above 100%. The keeper may wish to set an upper limit of (99+modifier)% to a skill.

The chief advantage of having a skill over 100% is that it lets you create a split dice pool and perform two actions instead of one. This is most applicable to combat. For example, someone with 108% in Handgun could choose to split their pool into two 54% chances (or a 99% chance and a 9% chance, whatever) and come out with two guns blazing like John Woo, or take two shots from the one gun where most people can only take one due to the recoil throwing off their aim, etc.

Skills above 100% can also make a difference when penalties are applied for especially difficult situations. A roll of 100 is still a failure.