Both these questions are covered in my draft FAQ; look at the section
### Measuring with IQ tests' at
http://community.haskell.org/~gwern/wiki/N-back%20FAQ.page For
people's convenience, I'll quote it below:
### Measuring with IQ tests
Because N-back is supposed to improve your pure '[fluid
intelligence](!Wikipedia)' (_Gf_), and not, say, your English
vocabulary, the most accurate tests for seeing whether N-back has done
anything are going to be ones that avoid vocabulary or literature or
tests of subject-area knowledge. That is, 'culture-neutral' IQ tests.
(A non-neutral test focuses more on your 'crystallized intelligence',
while N-back is supposed to affect 'fluid intelligence'; they do
affect each other a little but it's better to test fluid intelligence
with a fluid intelligence test.)
As one ML member writes:
> "The WAIS test involves crystallized intelligence and is unsuitable for judging fluid intelligence. High working memory will not spawn the ability to solve complex mathematical and verbal problems on its own, you have to put your extended capacity to learning. All very-high-level IQ tests are largely crystallized IQ tests, therefore working memory gains will not be immediately apparent by their measure."[](http://groups.google.com/group/brain-training/browse_thread/thread/8af44f3b20df9904)
The gold-standard of culture-neutral IQ tests is [Raven's progressive
matrices](!Wikipedia). Unfortunately, Raven's is not available for
free online, but there are a number of clones one can use - bearing in
mind their likely inaccuracy, and remembering that if you are testing
at the beginning and end of your training there is probably going to
be a [practice effect](!Wikipedia). They are:
- [iqtest.dk](http://iqtest.dk/main.swf)
- [A Spanish site](http://www.clipsite.com.ar/HOME/Salud/Test/Raven/)
- [Mensa Norway](http://mensa.no/olavtesten/#)
- [Quasi-ravens (unnormed?)](http://www.knowl.demon.co.uk/page111.html)
- [Queendom.com's "Culture Fair IQ
Test"](http://queendom.com/tests/access_page/index.htm?idRegTest=1112)
- <http://www.clipsite.com.ar/HOME/Salud/Test/Raven/Principal.asp>
- <http://www.iqtest.com/> (for-fee)
- [High IQ Society Online Test](http://www.highiqsociety.org/iq_tests/)
If Raven-style tests bore you or you've gone through the previous
ones, there are a wealth of difficult tests at Miyaguchi's
["Uncommonly Difficult IQ Tests"](http://www.eskimo.com/~miyaguch/).
--
gwern
The most famous open-source software is the operating system Linux (Do
you remember the commercials IBM ran a few years ago with the mob boss
instructing the teenager?) but the program you probably use the most
is the open-source web server Apache, which controls the operation of
2/3 of the world's web sites, and does a fine job of it.
The idea of Open-Source software is that it benefits from the creative
input of anyone who cares to contribute. Anybody who wants to can
download the program's human-readable source code and apply changes
(fix mistakes, add new features, etc) and submit those changes to be
included in the program in a later version.
This collaboration results in greater software quality from the number
of people who are able to check for errors, and the number of people
who are familiar enough with how the program operates to help other
users overcome problems.