Personality analysis in terms of parameters

how exactly is someone with a higher IQ different from someone with a lower IQ?

Start with the Wikipedia entry on 'Mental Retardation' and move toward the high IQ range. Many links to literature on differences between lower and higher IQ. Small degrees of IQ difference are hard to see, but large differences aren't.

Not from any particular literature: the range of errors that can be made by a high IQ person is greater than the range of errors that can be made by a low IQ person. A super-genius who can speak twelve languages and has degrees in physics and music can crash and burn in ways obvious to a casual observer. But an exceptionally low IQ person will never fail-up to learning twelve languages and having degrees in physics and music.

Judgement of other people can be pretty accurate actually. Observer judgement of the big five personality traits have more predictive power than self judgement.

See http://psycnet.apa.org/journals/apl/79/2/272/

Thin-slicing works well for judging Big Five. A paper just came out on detecting Big Five by correlation to choice of shoes, for example.

how *exactly* is someone with a higher IQ different from someone with a lower IQ?

I guess a higher IQ predicts a higher chance of solving a problem successfully; also solving the same problem in a shorter average time. The prediction works best for problems that are general enough (don't require too specific background knowledge), otherwise the domain knowledge becomes important too.

Is this the kind of answer you want?

It would be more exact with a specific way of measuring complexity of the problem (if everything else fails, we could just measure them by "how many people can solve this problem in one minute"), and then a two-dimensional table with IQ in rows, problem complexity in columns, and probability of solving the problems and average time in the cells. I never heard about something like this, so perhaps it would make a good thesis for a psychology student -- we just need a volunteer.

It would be interesting to know e.g. how much intelligence can be substituted by speed. For example if you give a person with IQ 150 one minute to solve a problem, and a person with IQ 100 gets unlimited time for the same problem, which kind of problem will give advantage to which one?

There are many different ways we could represent a personality (to varying degrees of accuracy.) I have not found a widely-accepted format, but I think we can each make our own for now. Whenever you wonder why someone acted a certain way, think about what the relevant parameters might have been and write them down. If several people work on this and share their results, perhaps one or more standardized personality representation formats will emerge.

The parameters collected by online user profiles such as those maintained by Facebook, Google Plus, or OkCupid might provide some inspiration.

If we had a good dataset of people and their personality attributes along with some performance measures, we could use machine learning to do neat things like predict relationship compatibility between two people. Imagine a rationalist dating service that used personality data to suggest matches!

Schema.org defines a "Person" model but it focuses primarily on circumstantial attributes rather than mental state.

There's probably a lot of low hanging fruit, for example use of correct priors, e.g. given Gaussian prior distribution, a quite strong proof should be needed before you should believe someone (including yourself) has very high intelligence or expertise on a task.

Furthermore, many ways of evaluating people are to some extent self reinforcing as the people being evaluated are aware of evaluation. A smart person or expert can relatively cheaply demonstrate intelligence and/or expertise, in some way that provides very strong evidence, and will do so even for relatively moderate payoffs. Likewise, very selfless people can cheaply (in terms of their utilons) help strangers, and will do so for lower payoffs than people with more selfish utilities.

Other issue is gradual updates on huge amounts of weak, possibly non-independent evidence.

I don't know about the others, but IQ is designed to have a mean of 100 and a standard deviation of 15. Whether or not the population actually matches that, I don't know for certain, but suspect strongly that it does not.