It stands for "Intelligence Quotient". IQ is calculated using a person's relative performance to their peers, this is known as deviation IQ. IQ itself is based on the g-factor, which can be expanded into Gf and Gc (fluid and crystallized intelligence) and the Cattell-Horn-Carroll theory (although others do exist, e.g, Parieto-frontal integration theory). It was once calculated using IQ = MA/CA x 100, which is no longer used. This may be why you see figures with absurdly high IQs, which is outdated and inaccurate.

It is probably the best figure for measuring intelligence, but the definition varies. The idea of IQ alone is appreciable in its own right; measuring a FSIQ predicated off the faculty of others on varied dimensions of cognitive aptitude should at least be indicative of something, especially if such a figure has been studied to be strongly associated to the variable components in life, more than any other test for intelligence that is.

g factor (also known as general intelligence) is the common variance across a range of cognitive tasks. It is derived from the Cattell-Horn Carroll Theory of intelligence which models cognitive ability hierarchically, with general intelligence or g at the top, broad abilities in the middle (FRI, VCI, CPI, etc.) and more specific abilities under that.

g-loading is the degree to which a test correlates with the g factor or general intelligence. A higher g loading means a test is better, and figures above 0.8 are generally considered to be great. g-loadings are often derived from a factor analysis. A g-loading may also be squared in order to derive the variance. For example, a test with a g-loading of 0.91 would mean that (0.91)^2 = 82.81% of the variance between test scores is due to g.

Reliability is the stability and consistency in the test scores, so if you take tests with high reliability under the same conditions then your scores are very likely to be stable.

Further Reading

It is known as Full Scale IQ. It is the most comprehensive measure of 'g' and is derived from compositing multiple subtests taken. You may see another index, such as the General Ability Index, where it focuses less on memory and processing speed. This can be useful for people who have a lower CPI relative to their other subtest scores due to autism, ADHD, etc.

Each of these indices are measures of different subsets of g, as defined by the Cattel-Horn-Carrol Model of Intelligence. These can be composited to calculate GAI or FSIQ. FRI stands for Fluid Reasoning, VCI stands for Verbal Comprehension, VSI stands for Visual Spatial, and QII stands for Quantitative Reasoning Index. CPI stands for Cognitive Proficiency and usually consists of WMI (Working Memory Index) and PSI (Processing Speed Index).

FRI is intimately related to PRI and FRI tries to measure inductive concepts such as matrix reasoning. It measures the underlying ability to figure out a conceptual relationship amongst visual objects, and then use reasoning to identify and apply rules. The FRI is typically composed of subtests such as Matrix Reasoning and Figure Weights.

VCI measures verbal concepts such as verbal reasoning. It can include both verbal knowledge and comprehension such as from drawing conclusions from verbal properties.

VSI measures the ability to evaluate visual details as well as the visual spatial relationships. The VSI could be tested from things such as Block Design and Visual Puzzles.

QRI measures the ability to reason and solve problems which involve quantitative information, such as through figuring out the patterns in a problem when expressed numerically. This is usually a subset of FRI.

It is mostly genetic, more than 75% of it can be attributed to genetics. FSIQ in adulthood can be ≈ 85% responsible. Furthermore, the differences between Verbal and Performance IQ can have specific differences (e.g., a source says 85% for the former and 69% for the latter). Now, environmental factors are stronger in earlier years where a developing brain is more volatile, but genetics will eventually be the dominating force as a person ages (Wilson Effect). Additionally, differences in the phenotypic IQ may come from environment, but this will often come from extreme changes in environment for the negative bound (e.g., extreme malnutrition/neglect).

No, by current knowledge, it is impossible to improve 'g'. It is possible to improve scores, but there will very likely be no significant physiological change where you will see any vast improvements in your actual IQ. IQ is more malleable when you are younger where the phenotypic expression for intelligence is more variable, so it is more important to ensure you have a healthy environment (sleep, diet, exercise, low stress) to foster your IQ to the greatest potential it could be. Obsessing over it will do little to change your IQ, in fact, it will probably contribute to lower scores due to a more negative state. Dual-N-Back literature is also quite conflicted, and the majority of professionals would reject the premise that any brain training program (e.g., Lumosity) would lead to any conspicuous changes. Your time is better spent working on individual skills than practicing something generalized like IQ and anticipating the change to be transitive inclusively for all cognitive realms. It is simply better to choose a subtopic and specialize in that when you are younger and more neuroplastic. Additionally, most drugs are also unlikely to reflect a significant change, but drugs like Cerebrolysin have been proven to help mitigate cognitive damage.

In general, IQ scores tend to remain relatively stable during adulthood, but they can change during different life stages. For instance, IQ scores tend to increase during childhood and adolescence, reaching peak levels in early adulthood. As individuals age beyond middle age, there might be a slight decline in certain cognitive abilities that are typically measured by IQ tests, such as processing speed, working memory, and fluid reasoning. However, crystallized intelligence, such as verbal comprehension, will continue to increase with age, plateauing roughly in the mid fifties.

The Wilson Effect states that IQ scores during childhood years tend to be unstable and are heavily influenced by environmental factors. "The broad heritability of IQ is about .40 to .50 when measured in children, about .60 to .70 in adolescents and young adults" (Jensen 1998, 169). However, as people approach later maturity, the impact of genetics takes over, reaching an asymptote of ~0.80 at 18-20 years old and remaining stable going forward. As age progresses, genetic influence on intelligence strengthens while environmental impact diminishes and your childhood scores may have been impacted by this. This may also explain the "gifted kid burnout" syndrome. Just as some were the tallest in their class as kids but stopped growing and are average height in adulthood, those who were "gifted" as kids may struggle to meet those same expectations as adults. However, the inverse may also be true, comparable to growth spurts.

See the resources list for trusted tests. Unfortunately, most professional tests are unavailable to take, however, there are many free tests linked in the Resources above that can be just as good as most professional tests.

The following free tests are the most recommended tests to take:

- The Old SAT and GRE are the most accurate measures of g but will take 2/3 hours to administer.

- AGCT is a fast and very accurate measure of g (40 minutes).

- CAIT is the most comprehensive free test available and can measure your Full Scale IQ (~70 minutes).

- JCTI is an accurate measure of fluid reasoning and recommended for non-native English speakers (due to verbal not being measured) and those with attention disorders (due to it being untimed).

Most online tests that can be found on Google are probably not good. However, there are trustworthy tests linked in this subreddit's resources tab, ranked by g-loading and other factors. Online administrations of leaked professional tests, such as those performed through Discord, are also accurate as long as the proctor follows the manual exactly and the examinee is in an optimal state, comfortable environment, and a strong connection. However, diagnoses from scores should be taken with a far larger grain of salt if they're by non-professionals. If you took a test in real life, ask your psychologist to interpret it first because they can do a better job than with our limited knowledge to your situation.

IQ is a measure of a person's ability comparative to everyone else. The scores are usually calibrated where 100 is the mean score or average. To put it in perspective, if you score 100 on an IQ test, you have an average intelligence quotient. Other ranges and classifications are typically around here.

The standard deviation, on the other hand, is a measure of variability. In the case of IQ tests, the standard deviation is the dispersion of IQ scores. A standard deviation of 15 means 68% of the population score an IQ within the interval 85-115 and 95% of the population scores within the interval 70-130. There are three different standard deviation scales, with 15 being the most popular and is associated with the Weschler tests, 16 is associated with the Stanford-Binet scale, and 24 with the Cattell scale. A common misconception from many is that when looking at scores without knowing the SD, if the SD is in 24, it would seem higher or lower than it actually is compared to an SD of 15 or 16.

The percentile rank of a score is the percentage of scores in its frequency distribution that are equal to or lower than it. For example, a test score that is greater than or equal to 75% of the scores of people taking the test is said to be at the 75th percentile rank. In order to convert an IQ score its corresponding percentile, you can use a normal curve calculator, such as this. You will always set the mean to 100 (unless the average IQ in a group is different), with the standard deviation set to the standard deviation of the test (Usually SD15 like the WAIS, but cases vary like how the Stanford Binet uses SD16 and the Cattell Culture Fair Test uses SD24), and the Standard Score "z" to the score received on the test. The percentile score returned represents the percent of the population you will score higher than.

No, it does not mean they are necessarily invalid, as long as it is sufficiently g-loaded, the conditions you took them in are not significantly disparate, and it was administered properly. They are often in the same confidence interval, or you are simply misinterpreting the test parameters (e.g., the standard deviation). Your IQ scores may differ based on the effects of age as well, explained above in the FAQ. Another reason why they may differ is that they are measuring different subsets of 'g'. For example, someone with strengths in VCI and weaknesses in PRI may score higher on verbal tests and lower in matrix reasoning tests. Depending on the types of tests you have taken, you can use the Compositator to get a comprehensive overview of your intelligence. Additionally, you can simply take an arithmetic or weighted average based on your scores.

Yes, they will usually be invalid. The g-loadings VCI tests are calculated and normed on native English speakers and will therefore not be accurate for non-natives. Unfortunately, due to the cultural nature of VCI tests, it is impossible to have a test that can accurately measure VCI for everyone. This isn't the case for other areas (e.g., FRI), where if directions are properly given, then the case is negligible.

It may be indicative of a neurobehavioral disorder, such as ADHD or ADD. There is no way to tell for sure, so professional input is greatly valued. Most studies indicate that ADHD itself does not lower IQ, but it will impact your cognitive function. Additionally, there is currently no direct evidence suggesting OCD impacts IQ, but the interference itself with cognitive function will affect performance on tasks requiring attention. Depression on the other hand has been proven to affect cognitive function in CPI related areas, such as memory and an overall permeating effect on executive function, but to quantify exactly how much it affects a score is a pointless endeavor.

Practically speaking, you should not let IQ discourage you too much from embarking on anything. However, it is true that IQ is indeed well correlated to certain occupations, and the effects do not necessarily plateau as you go higher. However, as a general rule, an IQ of 115 and above should suffice for most things, though if you go lower, one may expect more time invested in the fields. An IQ past the high 130s will not yield any considerable benefit for the majority of people. It is, however, still important for those in hyper-competitive areas, and there aren't any diminishing returns for those pursuing high-tier vocational levels, it is rather still advantageous. Regardless, the studies still consider the multidimensional aspects of this, considering other lifestyle factors as well.

You can take a variety of highly g-loaded tests, such as the old SAT, old GRE, or AGCT (of course the WAIS-IV and SBV are also great, but most people don't have access to them) and calculate your FSIQ. If your scores vary often amongst good tests (which they shouldn't too much), then you can either take a range of the scores or take a weighted average of them based on g-loading, or sometimes a simple arithmetic average may even suffice if all the tests are good, and a g-loading is not known.

If you know do the g-loading or correlation (they are interchangeable here) to a highly g-loaded test, then you can use the Big 'g' Estimator, available here.

Yes. It is important to consider practice effect yields do not correlate to any gains on 'g', as stated earlier. Some tests and item types are impacted by practice effect more than others.

Yes, the brain will always try to return to a baseline naturally after a form of serious trauma (for example, it has been proven that traumatic brain injuries can stimulate neurogenesis which leads to the proliferation of neural stem cells and synaptogenesis). Any form of exercise, such as aerobic and anaerobic are beneficial as they bring oxygen and blood to the brain (both together are best). Additionally, being and staying stimulated on skills you wish to excel in will help you by dint of synaptic pruning. The younger you are, the more likely you are to recover since you are more neuroplastic (for example, look at hemispherectomy recovery rates comparative to different ages). Getting proper sleep, will help with preventing the onset of neurodegenerative diseases such as Alzheimer's as cerebrospinal fluid will clear away metabolic waste (along with many other benefits as you sleep). Additionally, a good diet that is low in excessive fats is also good, along with a diet meeting recommended nutritional goals (Mediterranean diet is a good start). Staying stimulated and cognitively challenging yourself is also good. Social interaction has also been proven to help. To keep it short, diet, exercise, and sleep are the best for maintaining peak cognitive function and staving off neurodegeneration.

Genome-Wide Association Studies (aka GWAS) analysis can sometimes be quite accurate, and they work by identifying DNA variants that contribute to the variance in intelligence. Due to the strong genetic nature in IQ, GWAS can identify man single-nucleotide polymorphisms (SNPs) which have an effect on intelligence. The studies so far use a polygenic score which can be used to see how predictive it is of IQ. However, some studies find that Polygenic scores of intelligence can predict only around 4 to 10.6% of the variance in intelligence, so it isn't perfect.

This is an interesting question considering MBTI has been tested or inquired about in many scientific articles. The consensus is that MBTI itself lacks scientific rigor and exists purely as a commercial vessel, but that does not mean the score you get cannot be reliable nor accurate if MBTI were to adhere to strict definitions and scoring is dependent on a sample size and calibration of results. Another alternative would be the Big-5 which is perceived more positively than MBTI in academia.

No, not strongly that is. Fluency in chess is more indicative of training and taking advantage of the greater neuroplasticity and synaptic pruning one has in their younger years, although working memory and processing speed are likely to be the strongest factors related to high performance in chess (e.g., see the Polgars). Moreover, chess players such as Kasparov and Judit Polgar have both been testesd, and Kasparov scored the highest at 135 when he was tested by a magazine that employed psychologists. The strongest correlation is likely CPI compared to the rest.

Most likely not, but it is impossible to say for certain. The test in which Feynman scored 125 on was as an adolescent in high school, meaning his scores are not representative of his capabilities as an adult. We also cannot determine whether or not the test was a verbal test or a full-scale test, though it is heavily speculated it was a verbal test, meaning measurements of Feynman's strong fluid reasoning skills were likely neglected. “According to his biographer, in high school the brilliant mathematician Richard Feynman's score on the school's IQ test was a ‘merely respectable 125’ (Gleick, 1992, p. 30). It was probably a paper-and-pencil test that had a ceiling, and an IQ of 125 under these circumstances is hardly to be shrugged off, because it is about 1.6 standard deviations above the mean of 100. The general experience of psychologists in applying tests would lead them to expect that Feynman would have made a much higher IQ if he had been properly tested.” John Carroll (1996), The Nature of Mathematical Thinking (pg. 9). His IQ is most likely much higher than 125, but it's impossible to know by how much due to lack of information.

These figures were calculated using the values in their respective manuals and studies.

These were calculated using values from IQExams.

^ means the distribution may not be normal, so interpret the values with caution.

Results for all tests and tiers were calculated around 1/08/2022 to 4/18/2022 and are subject to being altered if more data is provided (likely not)