A crystallized intelligence test, from vocabulary to verbal reasoning

0 The short answer

A crystallized intelligence test measures comprehension-knowledge (Gc), the depth and breadth of acquired knowledge and language based reasoning, and the version worth taking reports a normed index with a confidence interval instead of a quiz tally. A psychologist can give a Wechsler or Woodcock-Johnson battery in a supervised session, and ACIS offers five verbal subtests (Antonyms, Vocabulary, Information, Synonyms and Similarities) that the Custom Test returns as a Verbal Comprehension Index for 25 dollars (prices read October 29, 2026). The Full Scale form, 50 dollars and about 175 minutes, contains all five. The decisive limit is that Gc depends on the language and schooling you were tested in, so an online, unsupervised, English only index describes your standing on those tasks and cannot diagnose or certify anyone.

1 What does a crystallized intelligence test measure?

A crystallized intelligence test measures what a person has learned and can put to use through language, and "crystallized IQ" is a search phrase rather than a standard score category. The term goes back to Cattell, whose 1963 paper in the Journal of Educational Psychology carries the title "Theory of fluid and crystallized intelligence: A critical experiment." In the Cattell-Horn-Carroll (CHC) model that grew from that tradition, the broad ability is called comprehension-knowledge and abbreviated Gc. The page on the CHC model lists the broad abilities and the narrow abilities beneath each.

Test publishers define Gc in similar words. Riverside Insights, publisher of the Woodcock-Johnson V, describes it in its test descriptions for the cognitive battery, read October 29, 2026, as "originally described as crystallized intelligence," including the depth and breadth of acquired knowledge, the ability to communicate that knowledge, and the ability to reason using previously learned experiences or procedures. The same document says this store of knowledge is primarily language based and has developed largely through education and general life experience. The ACIS technical manual, read on the same date, uses a close definition: depth and breadth of acquired knowledge, verbal concepts and language based reasoning.

Three ideas sit inside that definition. The first is stored word knowledge, which tests call lexical knowledge. The second is stored factual knowledge, the kind that comes from schooling, reading and conversation. The third is verbal reasoning that works on learned concepts, such as seeing what two different things have in common. A test that samples only one of the three covers part of Gc. Baghaei and Tabatabaee, writing in the Journal of Intelligence in 2015, state that crystallized intelligence "is usually measured by means of vocabulary tests and other verbal tasks," which is why a vocabulary quiz is often sold as a crystallized test and why a full battery asks for more.

Ackerman's 1996 paper in Intelligence is titled "A theory of adult intellectual development: Process, personality, interests, and knowledge," and the title names knowledge alongside process, personality and interests as parts of the theory, which is one reason knowledge tests matter beyond testing itself. The practical consequence for a test taker is that a Gc score is partly a record of where your time and curiosity went, which the section on what builds Gc returns to.

Gc is not the same thing as general knowledge in a narrow sense, and it is not the whole of intelligence. The page on intelligence versus knowledge separates reasoning ability from stored learning, and the CHC page lists how Gc sits among the other abilities in a battery.

2 Which tasks does a crystallized intelligence test use?

A Gc battery uses four task families, vocabulary, lexical relations, general information and verbal concept formation, and a fifth, verbal analogies, sits between Gc and fluid reasoning. The families differ in what they ask for and in how the answer is given, and the format changes what a low score can mean.

Vocabulary tasks ask what a word means. They come in two formats. In the production format the person writes or says a definition and an examiner or a scoring rule grades its precision. In the recognition format the person picks the best meaning from a list. The ACIS manual describes its Vocabulary subtest as the first kind: the examinee is shown a word and types its definition in their own words, with credit graded on precision and completeness. The page on the vocabulary IQ test compares the two formats and how closely vocabulary tracks general ability.

Lexical relation tasks ask which word means the same as, or the opposite of, a target word. The manual describes Synonyms as selecting the option closest in meaning, and Antonyms as selecting the word most nearly opposite. Because the answer is chosen rather than produced, the manual notes, the demand is recognition of a meaning relation, not the ability to define the word. Riverside's Woodcock-Johnson V document describes its Oral Vocabulary test the same way, as two subtests, Synonyms and Antonyms, each measuring an aspect of the vocabulary knowledge of spoken English.

General information tasks ask factual questions that schooling and everyday exposure usually answer. The Woodcock-Johnson V document describes a General Information test with two parts, one on where things are found and one on what to do with them, and tags it to general knowledge within Gc. The ACIS manual describes its Information subtest as typed answers to general knowledge questions, drawn from knowledge ordinarily acquired through schooling and everyday exposure rather than specialized study, with a short fixed interval per question. The page on the general knowledge IQ test explains why a trivia score and a normed information score are different things.

Verbal concept formation tasks ask how two things are alike. The ACIS manual describes Similarities as producing an explanation of how two words are alike, with graded credit: a superordinate category earns full credit and a concrete or functional resemblance earns partial credit. The manual says this scoring distinction is what separates induction from lexical knowledge alone. That is why Similarities is a Gc subtest with a bridge to reasoning, and the section on fluid reasoning below returns to it.

Verbal analogies sit on the border. In the Woodcock-Johnson V document the Verbal Analogies test is tagged to both Comprehension-Knowledge (Gc) and Fluid Reasoning (Gf), with lexical knowledge and induction as its narrow abilities. A reader whose question is about analogy items in particular will find them treated on the page about the analogies IQ test.

A fifth format deserves a mention because it shows how wide the construct is. Baghaei and Tabatabaee argue that a text completion task, the C-Test, taps the language component of crystallized intelligence, and that texts from chosen knowledge domains could extend it to the factual component. That is an argument in a journal article, not an established battery subtest, and it is cited here to show that a Gc score depends on the task that produced it. When a page claims to offer a crystallized test, the first question is which of these families it samples, and the page on the verbal IQ test covers how a verbal score is built when several are combined.

No section of this page reproduces items or lists test words, and the subtest pages and the manual describe formats only.

3 What are the options for taking a crystallized intelligence test?

You can take a Gc test from a psychologist, from a free quiz, from a hiring vendor or from a normed online battery, and the options differ more in what they report than in how their questions look. The table sets them side by side. ACIS prices and times were read on October 29, 2026 and can change. Cells marked "not stated" mean the source read gave no figure.

The clinician route is the reference. Pearson's WAIS-5 product page, read October 29, 2026, lists the test as published in 2024, qualification level C, with the print kit at 1,784 dollars and administration times of 45 and 60 minutes for the two scoring routes. It also lists "new crystallized and fluid expanded index scores" among the features. Pearson's overview brochure shows the Verbal Comprehension scale with four subtests in the full scale (Similarities, Vocabulary, Information and Comprehension) and two on the primary index scale (Similarities and Vocabulary), and names a "Verbal Expanded Crystalized Index" among the expanded scores, with Pearson's spelling. The kit price is what a professional pays, and the fee for an assessment is set by the clinician.

Free quizzes answer a different question. They are entertainment or screening, they usually return a count or a label, and many do not state a norm group. The page on free IQ tests explains what a free result can and cannot support. Hiring vendors sell verbal reasoning tests for selection, which are not IQ indexes and fall outside this page.

ACIS is a seller in this market, so treat this section as a disclosure. The table shows where the options differ: only the clinician route is supervised and clinically interpreted, and the Wechsler and ACIS routes report a normed index. Other online batteries exist, and the page on the best online IQ tests and the page on where to take an IQ test compare them without a focus on Gc. A reader who wants a broader screen of several abilities at once can start from the page on the cognitive ability test.

4 What does the ACIS Verbal Comprehension Index consist of?

The ACIS Verbal Comprehension Index (VCI) is built from five subtests, Antonyms, Vocabulary, Information, Synonyms and Similarities, and each samples Gc through a different format. All five are reported as scaled scores from 1 to 19 (mean 10, standard deviation 3), and together they yield the index on the scale with mean 100 and standard deviation 15, with a percentile and a 95 percent confidence interval. Each subtest has its own page, and the pages describe the construct without disclosing items.

The Vocabulary page frames the task as how precisely a person understands words and how well those meanings can be explained or recognized, and notes that word knowledge grows through years of reading, schooling and conversation. In the manual the examinee types a definition in their own words under a limit of 1 minute 30 seconds per item. The Antonyms page describes precision in word meaning, whether a person can separate a term from its opposite. In the manual this is a multiple choice section of 31 words under one continuous 10 minute limit, so distributing effort across items is part of the task. The Synonyms page describes meaning equivalence, and the manual gives it 31 questions in a 10 minute whole section limit, with single word stimulus and options so that sentence context cannot help.

The Information page describes general knowledge accumulated over time and retrieved without lengthy problem solving. In the manual the answers are typed, there are 30 questions, and each advances automatically after 30 seconds, which keeps the subtest a measure of information already held rather than of reasoning time. The Similarities page describes verbal concept formation, and the manual gives it 31 pairs at 1 minute 30 seconds per item with credit from 0 to 2 points. The pages and the manual state no total administration time for the five together, so none is given here. None of the five is among the three subtests that present items as audio, so working sound is not a requirement for this index, though a quiet room still helps.

The manual also gives reading rules for the pattern across the five. If Information is high with Vocabulary and Synonyms, the profile supports broad verbal knowledge strength, and if Information is lower than Vocabulary the person may have strong word meaning but narrower factual exposure. If Antonyms is high and Similarities lower, the profile may show strong word knowledge with less semantic relation reasoning. A weak Synonyms score beside adequate Vocabulary may point to fine grained meaning discrimination or unfamiliarity with specific word forms rather than a broad verbal limitation. These are descriptions of profile shapes, not diagnoses, and each depends on every score carrying its own uncertainty.

Which form contains which subtest decides what the report can show. The manual's availability table says Quick (15 dollars, about 45 minutes) holds two of the five, Similarities and Vocabulary, and reports a partial verbal index. Optimized (30 dollars, about 110 minutes) holds four, all but Information, also a partial index. A full VCI requires all five, which the Full Scale form (50 dollars, about 175 minutes) contains. The manual lists a composite called VKI that "combines Antonyms, Synonyms, Vocabulary, and Information," available on the Full Scale form because it needs those four subtests. The Custom Test, at 5 dollars per subtest, lets a buyer pick any subtests, and its description states that "any domain you complete returns its full index score, and every subtest returns its scaled score." Five verbal subtests at 5 dollars each is 25 dollars, our arithmetic on the posted price. The Full Scale form costs the same as ten Custom subtests, so a buyer who wants more than ten should take the Full Scale form.

The free trial needs no card and is limited to one per person. As read on the site on October 29, 2026, it does not return a Verbal Comprehension Index, so the Custom Test is the direct path to this index. The technical manual holds the full definitions, and this page quotes no statistics from it.

5 How is crystallized intelligence different from fluid reasoning?

Crystallized tasks ask what you already know and can say about it, while fluid tasks ask you to solve a problem you have not seen before, and the two blur at the edges where a learned concept has to be used to reason. The page on fluid versus crystallized intelligence owns the full comparison, so this section covers only what matters when choosing a test.

The ACIS manual defines fluid reasoning as reasoning and problem solving in novel situations through induction, general sequential reasoning and flexible adaptation, "without relying mainly on learned knowledge." The Woodcock-Johnson V document likewise describes Gf as reasoning with unfamiliar information or novel procedures. The Wechsler scale also reports the two apart: Pearson's WAIS-5 product page lists separate visual spatial and fluid reasoning indexes, and the brochure shows a Fluid Reasoning scale beside Verbal Comprehension. In ACIS the fluid domain has its own Fluid Reasoning Index, and the page on the fluid intelligence test covers what those tasks measure.

The edges are real. The manual says a semantic relation item may involve both lexical knowledge and induction, and it lists Similarities under induction as well as lexical knowledge. Riverside tags its Verbal Analogies test to both Gc and Gf. So a high Similarities score does not by itself tell you whether the strength lies in stored concepts or in the ability to see a rule, and the answer comes from the other subtests around it.

For a test taker, the useful comparison is the verbal index against the fluid index in the same battery. A gap between them describes a pattern of strengths and does not say why the pattern exists. The page on how often index scores differ gives the context a single gap needs, because uneven profiles are common and are not a defect.

6 How does crystallized intelligence change across adulthood?

Measures of acquired knowledge, especially vocabulary, peak later in adulthood than speeded and memory tasks, but the exact age depends on the sample and the era, so no single peak age should be treated as a rule. The best open evidence is Hartshorne and Germine's 2015 paper in Psychological Science. Its abstract reports convergent evidence from 48,537 web participants and a comprehensive analysis of normative data from standardized IQ and memory tests, with "considerable heterogeneity" in when abilities peak: some peak around high school graduation, some plateau in early adulthood and decline from the 30s, and "still others do not peak until the 40s or later."

The normative part of the study used the WAIS-III standardization sample, 2,450 healthy Americans aged 16 to 89. The authors report that the five tasks invoking learned knowledge (vocabulary, information, comprehension, arithmetic and similarities) peaked significantly later than nearly every other task. In their web experiments they compared three tasks directly, and the three peaked in the order digit symbol coding (late teens), digit span (early twenties) and vocabulary (around 50) in the WAIS-III data, which means average vocabulary performance in that sample was still rising at 40. That ordering is why the pages on processing speed and on short term memory belong beside this one: the abilities that rise first are not the ones a Gc battery measures, and a person whose speed or span is past its peak can still be gaining on word and knowledge tasks.

The paper is also candid about limits. In its web data the vocabulary peak came later, at about 65, than in the WAIS-III data, at about 50, and the authors say this could point to confounds in one or both datasets or to cohort differences, since the Wechsler data were collected two decades earlier. Both datasets are cross-sectional, meaning different people were tested at different ages, so an age pattern can mix aging with generational change. The authors argue that cohort effects cannot explain the order in which the three tasks peaked, because the order replicated across datasets. The reasonable reading is that learned knowledge tends to keep growing well past the age at which speed peaks, and that the number attached to that peak moves with the sample.

Vocabulary size gives a sense of the scale of what accumulates. Brysbaert and colleagues, in Frontiers in Psychology in 2016, estimate that an average 20-year-old native speaker of American English knows 42,000 lemmas and that between ages 20 and 60 the average person learns about 6,000 more, roughly one new lemma every 2 days. A lemma counts a word and its inflected forms as one, and the title of the paper says the estimates depend on how a word is defined, on language input and on age. The study tested 221,268 individuals over 265,346 sessions, so the figures are population averages from a web sample, not a measurement of any reader.

What this means for a score is that age matters to the reading of a verbal result. The ACIS Synonyms page says a verbal result is read against an age reference rather than a single fixed standard, and the page on average IQ by age explains how age norms work. Readers past middle age will find the age related picture, and the case for testing the abilities that do and do not change, on the page about the IQ test for adults over 40.

7 What builds crystallized intelligence, and what does that mean for a score?

Crystallized intelligence is built by schooling, reading and time spent with language, which makes a Gc score partly a record of exposure and not a pure measure of capacity. Three bodies of evidence bear on this, and each has a design that limits what can be said.

The first is education. Ritchie and Tucker-Drob, in Psychological Science in 2018, meta-analyzed quasi-experimental studies of education and intelligence. Across 142 effect sizes from 42 data sets with over 600,000 participants, they found consistent evidence for beneficial effects of education on cognitive abilities of approximately 1 to 5 IQ points for an additional year of education, with effects that persisted across the life span and were present on all broad categories of cognitive ability they studied. The result is about cognitive abilities in general, not Gc alone, and it describes group averages from designs that approximate experiments.

The second is reading. Cunningham and Stanovich, in Developmental Psychology in 1997, followed first graders to the 11th grade. First grade reading ability predicted all the 11th grade outcomes, which included vocabulary and general knowledge, and it remained a predictor when measures of cognitive ability were partialed out. They also found that individual differences in exposure to print predicted differences in growth of reading comprehension. This is an observational study, so it supports an association between early reading and later knowledge and does not show that a reading program would raise a particular person's score.

The third is theory. Ackerman's 1996 theory, whose title names knowledge among its components, is consistent with the idea that what a person has learned depends on where effort and curiosity were invested, and so are the two studies above. The ACIS manual says the same of Information, which depends on exposure, education, curiosity, reading and cultural context and must be interpreted with caution when used in isolation.

For a test taker this has three consequences. A Gc score can rise over a lifetime without any change in reasoning ability. A low score on a knowledge task can reflect limited exposure, a narrow educational history or language background, as the Vocabulary page says, and not a limit on ability to learn. And a score describes standing at the time of testing, not a ceiling.

One boundary needs stating because the literature blurs it. Hartshorne and Germine counted Arithmetic among the learned knowledge tasks, but ACIS places Arithmetic in its quantitative reasoning domain, not in the verbal domain, and its quantitative subtests are covered on the page about the mental math test.

8 How do language and culture change a crystallized intelligence score?

A Gc score is a score in a particular language and culture, so a test given in English measures English based Gc, and a reader who learned English later should read it as exactly that. The Riverside Woodcock-Johnson V document says the store of knowledge in Gc is primarily language based, and the ACIS technical manual says Gc is strongly affected by English proficiency, educational exposure and cultural knowledge. Its list of limits for online testing says that verbal and knowledge tasks can be affected by English proficiency and educational exposure, and its description of Vocabulary says the subtest is language and culture sensitive, which is why interpretation must respect the English speaking norm frame.

The research on bilingual vocabulary shows the same mechanism in children. Bialystok, Luk, Peets and Yang analyzed 1,738 children between 3 and 10 years old in Bilingualism: Language and Cognition in 2010 and reported a consistent difference in receptive vocabulary between bilingual and monolingual children in the language of testing. Two preliminary analyses suggested that the difference did not change with different language pairs and was largely confined to words relevant to a home context rather than a school context. The study concerns children, and carrying the principle to adults is our inference: the score reflects which words a person has met in the language of the test.

The Standards for Educational and Psychological Testing frame the issue as construct relevance. Standard 3.2 makes test developers responsible for minimizing the effect of construct-irrelevant characteristics, such as linguistic and cultural ones, on scores. In a Gc test, knowing the language of the test is part of the construct being measured, so the real question is which construct the reader wants. A person whose first language is Spanish and who takes an English test gets an estimate of English based Gc, not of knowledge across both languages. The page on the IQ test for non-native English speakers covers what moves in such a score and which parts of a battery move least.

Culture works through content as well as words. Information samples knowledge ordinarily acquired through schooling and everyday exposure, and what counts as everyday depends on where a person lived and studied. The ACIS pages say a weak result on these tasks may reflect reduced exposure, a different educational history or a cultural or language background. A practical rule follows: read the verbal index against the fluid and working memory indexes in the same battery, and read a gap as information about exposure and language before reading it as information about ability.

9 How should a crystallized intelligence score be read?

A Gc score is read as a position on an age referenced scale with a stated margin of error, and the pattern across subtests carries more information than any single number. ACIS reports each verbal subtest as a scaled score from 1 to 19 with mean 10 and standard deviation 3, and the Verbal Comprehension Index on the familiar scale with mean 100 and standard deviation 15. The page on why the standard deviation is 15 explains that choice, and the page on how IQ scores are normed explains what a norm group does.

A percentile restates the index as a rank. On a normal curve with mean 100 and standard deviation 15, an index of 100 sits at the 50th percentile, 115 at about the 84th and 130 at about the 98th. That is our arithmetic on the normal curve and not a table lookup, and any reader can check the conversion. The 95 percent confidence interval is the range within which the person's true standing is expected to lie given measurement error, which is why two indexes a few points apart usually do not differ in any meaningful way.

Measurement error is the reason one subtest is less precise than a battery. The Standards for Educational and Psychological Testing (AERA, APA and NCME, 2014), in Standard 2.13, say the standard error of measurement should be provided in the units of each reported score, which is why an index reported with an interval is more informative than one reported without. A single 10 minute section samples a small number of words, while an index built from five different formats averages over several kinds of error. The page on reliability and validity explains the terms in plain language, and the technical manual documents the numbers, which this page does not quote.

Three reading rules apply to Gc in particular. First, a partial index from the Quick or Optimized form is built from fewer subtests than the full index, and the manual labels it as partial. Second, the five verbal subtests return a Verbal Comprehension Index and not a Full Scale IQ, which needs the Full Scale battery. Third, compare the profile before the headline. The manual's rules, covered earlier, tie each pattern to a possible cause such as narrower factual exposure or less semantic relation reasoning, and every one of them is a hypothesis that the full profile and the reason for testing must confirm.

10 What conditions help an unsupervised crystallized intelligence test give a fair score?

An unsupervised Gc test is fair to the extent that the person answers from memory, without lookups, in the language of the test and within the time limits. Looking up a word or a fact, asking an assistant or searching during the test would change what the score measures, because the score would then describe the tool and not the person. The tasks here are timed to discourage this: the manual gives 10 minutes for each of Antonyms and Synonyms as a whole section, 30 seconds per question for Information, and 1 minute 30 seconds per item for Vocabulary and Similarities.

Vocabulary and Information answers are typed and Similarities answers are produced, so a working keyboard and a screen that shows the full item matter. The technical manual notes that online administration requires careful interpretation and that it cannot eliminate every environmental influence. The conditions within a reader's control are modest: a quiet room, a rested state and a block of time long enough that the clock does not force hurried answers.

The form allows breaks, saves progress between subtests and gives 30 days to complete, so there is no need to push through fatigue. A person who is reading English with effort should not treat the verbal subtests as a speed contest, and should take them when reading feels comfortable. The subtest pages and the manual describe formats only and keep operational content private.

11 What can a crystallized intelligence score be used for, and what can it not?

A Gc score is useful for understanding your own profile of verbal knowledge and reasoning, and it is not evidence for a decision about hiring, school accommodations, admission to a high IQ society or a clinical question. The ACIS limits are stated plainly: the test is online and unsupervised, it is not a clinical or diagnostic instrument, and it is not for hiring, school accommodations or admission to high IQ societies.

Within those limits, a verbal index is informative in three ways. It shows how a person's acquired knowledge and language based reasoning compare with adults of the same age. It shows, beside the other indexes, whether the verbal side of the profile is a strength or a relative gap. And it can open a conversation with a professional if a reader has a real question about learning or language. A reader who wonders whether a strong verbal result points to a gifted profile will find the framing, and its limits, on the page about the gifted test for adults.

Group statistics do not apply to the individual. The lifespan studies cited above describe average performance at each age in large samples, and the education and reading findings describe averages and associations. None of them says what any one reader's score should be, and none supports a claim about a reader's health or future. A high Gc score does not imply high fluid reasoning, and a modest Gc score in a second language does not imply low ability. The right use of the number is as one measurement, with its margin of error, taken on one day under stated conditions.

12 Where ACIS sits, and what a buyer should do

ACIS offers a five subtest Verbal Comprehension Index with adult norms for ages 16 to 90 at 25 dollars, and it is an online, unsupervised, non clinical, English only instrument whose score should be read with those limits in view. ACIS sells these tests, so this section is a disclosure and the table above should be checked against it. Prices were read on October 29, 2026 and can change.

The strengths are specific. The index is built from five formats that cover word knowledge, lexical relations, general information and verbal concept formation, rather than from a single vocabulary quiz. It comes with a percentile and a 95 percent confidence interval, the payment is one time with no subscription, progress is saved, and a buyer has 30 days to finish. The guarantee reads: "Full refund within 5 days if the report does not deliver the features described at checkout or a technical issue prevents you from accessing your results." That is a conditional guarantee and not an unconditional money back promise.

The limits matter as much. The test is online and unsupervised, so conditions are not verified, and a clinician cannot observe the session. It is English only, and the manual says verbal and knowledge tasks are affected by English proficiency and educational exposure. It is not a clinical or diagnostic instrument, and it is not for hiring, school accommodations or admission to high IQ societies. The Optimized form returns a partial index that omits Information, the Quick form returns a partial index from two subtests, and only the Full Scale form returns the full index together with the Full Scale IQ and the other composites.

The Standards for Educational and Psychological Testing (AERA, APA and NCME, 2014) bear on exactly these limits. Standard 3.15 says developers who claim a test can be used with specific subgroups are responsible for supplying the information that supports interpretation for those subgroups, and its comment asks for explicit statements about applicability and cautions against foreseeable misuse. Standard 3.16 says that when credible research indicates scores are differentially affected by construct-irrelevant characteristics, test users should use the test only for the subgroups for which there is sufficient evidence of validity. Standard 5.1 says test users should be provided with clear explanations of the characteristics, meaning and intended interpretation of scale scores, as well as their limitations. This page applies that reading: the English frame is stated, the limits are stated, and the technical manual is the place for the documentation.

The American Psychological Association gives psychologists the matching guidance in its Ethical Principles of Psychologists and Code of Conduct, effective January 1, 2017. Standard 9.02(c) asks psychologists to use assessment methods appropriate to an individual's language preference and competence, and Standard 9.06 asks them to take into account linguistic and cultural differences that might reduce the accuracy of their interpretations and to indicate any significant limitations. Those standards bind psychologists, not a self administered online test, but they set the benchmark for how any Gc score should be read.

What to do next depends on the question. If the question is only about verbal knowledge and reasoning, the Custom Test with the five verbal subtests at 25 dollars returns the full index. If the question is how the verbal index compares with fluid reasoning and the other domains, the Full Scale form at 50 dollars returns all six indices and the Full Scale IQ with its interval. Look at an example report before paying, remember that the free trial shows the platform without returning a verbal index, and read the English language limit as a real condition: if English is not your first language, treat the result as an English based Gc score.

13 Sources Behind This Page

Every figure above is traceable to one of the following, and each is linked at the point where it is used. Web pages were read on October 29, 2026. The percentiles in the score reading section and the 25 dollar total are our arithmetic on a normal curve and on the posted Custom Test price, and are labeled as such in the text.

• Ackerman P. A theory of adult intellectual development: Process, personality, interests, and knowledge. Intelligence, 1996, volume 22, issue 2, pages 227 to 257.
• AERA, APA and NCME. Standards for Educational and Psychological Testing. American Educational Research Association, 2014.
• American Psychological Association. Ethical Principles of Psychologists and Code of Conduct, effective January 1, 2017, Standards 9.02 and 9.06.
• Baghaei P and Tabatabaee M. The C-Test: An Integrative Measure of Crystallized Intelligence. Journal of Intelligence, 2015, volume 3, issue 2, pages 46 to 58.
• Bialystok E, Luk G, Peets K and Yang S. Receptive vocabulary differences in monolingual and bilingual children. Bilingualism: Language and Cognition, 2010, volume 13, issue 4, pages 525 to 531.
• Brysbaert M, Stevens M, Mandera P and Keuleers E. How Many Words Do We Know? Practical Estimates of Vocabulary Size Dependent on Word Definition, the Degree of Language Input and the Participant's Age. Frontiers in Psychology, 2016, volume 7, article 1116.
• Cattell R. Theory of fluid and crystallized intelligence: A critical experiment. Journal of Educational Psychology, 1963, volume 54, issue 1, pages 1 to 22.
• Cunningham A and Stanovich K. Early reading acquisition and its relation to reading experience and ability 10 years later. Developmental Psychology, 1997, volume 33, issue 6, pages 934 to 945.
• Hartshorne J and Germine L. When Does Cognitive Functioning Peak? The Asynchronous Rise and Fall of Different Cognitive Abilities Across the Life Span. Psychological Science, 2015, volume 26, issue 4, pages 433 to 443.
• Pearson. Wechsler Adult Intelligence Scale, Fifth Edition (WAIS-5) product page, read October 29, 2026.
• Pearson. WAIS-5 overview brochure, read October 29, 2026.
• Riverside Insights. Woodcock-Johnson V Tests of Cognitive Abilities: Test Descriptions, read October 29, 2026.
• Ritchie S and Tucker-Drob E. How Much Does Education Improve Intelligence? A Meta-Analysis. Psychological Science, 2018, volume 29, issue 8, pages 1358 to 1369.

14 Frequently Asked Questions