Default Skill Theory
 

Why are default penalties set as they are, for example -5 to average difficulty skills?

Knowing how much thought went into GURPS, I suspect that a -5 default penalty to average skills was not arbitrary, but probably chosen with a rationale (and a mathematical one at that). Looking at the probabilities on B171, I see that someone with a 10 default attribute, or 50% probability of success, will roll against a 5 for an average default skill. Moreover, the probability of rolling a 5 or less is roughly 5% (1/10 the probability of the associated attribute). the ratio does not remain static, however. Since someone with an 11 skill (62.5%) would roll against a 6 (roughly 10%), although at 15-16 the ratio returns to roughly 50%, and at 17-18 swells to much better than 50% for a default skill.

As someone who likes to host and run games, I like to understand the rationale behind the rules in order to better explain them to the players.

Re: Default Skill Theory
 

Yes, due to the 3d6 bell curve improvements to skill help the most in the middle of the curve. This generally makes a lot of things in GURPS just work out really well, because it's a close approximation of the normal distribution, which ends up just being a good fit model for all kinds if things.

Note also though that GURPS skills assume use in an adventuring situation. Which is really not when you want to be trying something you aren't trained for! In situations where people are more comfortable attempting a default (e.g. learning to drive in an empty parking lot) you probably should be giving a generous positive task difficulty modifier, see B345.

Re: Default Skill Theory
 

Let's look at driving. The average untrained driver has about a 50/50 shot at commuting to work in a small town. They've got pretty much no chance at successfully chasing another car. But on the other hand, they're pretty much guaranteed to be able to drive around an empty parking lot or turn the car on.

If I had to guess, the defaults were set up to ensure that the average person is basically guaranteed to accomplish really easy tasks, fail the tasks an adventurer takes on, and have a risk comparable to an adventurer if the task is in-between.

The fact that boosting DX or IQ makes you much better at a whole bunch of simple tasks is an artifact of the system having stats that apply to everything.

Re: Default Skill Theory
 

Most of us would be at driving skill 10-12 and usually working with hefty bonuses. The majority of driving would be at like +5 for people that have been doing it for awhile. Inclement weather would lower that, but that can be countered with driving at lower speeds. Stunt drivers would be at skill 15+.

Re: Default Skill Theory
 

My assumption for the skills defaults is that, if there was a basis other than "this seems to work about right" whenever they were created, it's that a character using an Easy skill at default (Attribute-4) for a routine task (+4 TDM) rolls against unmodified Attribute to do it.

Re: Default Skill Theory
 

This is brilliant. I hadn't thought of that but it feels accurate.

Re: Default Skill Theory
 

I did a short Pyramid article listing a whole lot of things you could do with various skills whose ease modifiers brought an untrained character up to "roll vs. stat."

Re: Default Skill Theory
 

Now it occurs to me that since players cannot roll a skill the effective skill of which falls below 3, -5 approaches the lowest possible value. In fact, a character with an 8 in an attribute could not make a default roll on a hard skill that defaults to that attribute.

Re: Default Skill Theory
 

For adult humans attributes that low represent pretty severe disabilities.

Re: Default Skill Theory
 

Might want to list the article when you mention that :)
I dont recall it but should add a reference to it on my Skill Primer page.