The reverse digit span test, a common part of modern standard IQ tests that can be used to measure IQ on its own.
Reverse digit span is another task that comes from psychology. It’s a standard IQ test, often used as part of a battery of tests. But since every part of IQ correlates very strongly with every other part, it’s okay to use on its own (albeit with bigger error bars). What’s really interesting is that it’s cross-cultural (although not perfectly) and extremely cheap to administer – that is, so cheap it can be automated, and somewhat bizarrely has not been put online for free administration (as far as I can tell), until now.
First, to explain the test. You are given a series of numbers, one at a time, and have to recite them back to the test administrator in reverse order (due to the reverse order, it should be obvious you can’t start until the administrator is finished). You keep going until the sequence is too long and you can’t do it correctly anymore.
So, as long as you are familiar with Arabic numerals, there isn’t too much context-specific knowledge, and it’s absurdly easy to translate the instructions to other languages. Ideally, familiarity with numbers shouldn’t be assumed – we’d want accurate IQ scores for people without any access to education or literacy training. For those groups, or for groups such as the exceptionally young who may not be able to communicate verbally or in writing at all, we can use a test called Raven’s Progressive Matrices, which is a more pure pattern-recognition test that can be taken by only pointing or grabbing the answers.
Normally, that’d be the end of the testing discussion. Raven’s Progressive Matrices are really quite perfect for almost any use.
Except if you want to see if improving nutrition improves IQ over someone’s lifetime, where it’s hard to use, or if you want to see how stable IQ is over someone’s life, where it’s impossible to use.
The reason it’s such a bad match for those use cases is that the matrices are hard to create. Imagining a pattern and thinking of other things that don’t fit what that pattern could be is hard, and most people would make very slight variations on a theme. But if you’ve seen an almost identical question years ago, the results for taking the test today would be nearly worthless. You could be using your mind to pattern match, or just be remembering the pattern. Often, people will remember things they are familiar with without noticing.
These tests are where the reverse digit span test (or backwards digit span test, as some prefer to call it) comes in. Due to the mere exposure invalidating Raven’s Progressive Matrices, it’s also probably the best IQ test that can be administered publicly without goofing other researcher’s data (which would be exceptionally rude). I can make up a new sequence of digits extremely easily, so there’s no concern that participants would learn anything they don’t hear about in the instructions.
The only thing I don’t know are the details of how the test is administered, weighted and converted to IQ. I’ve supplied what I know on the scoring page, though. For those curious, I typically score about 10, but don’t know any of the cool mnemonics yet.