What the cognitive proficiency index combines and what a GAI gap means

0 The short answer

The Cognitive Proficiency Index (CPI) is a composite score that combines working memory and processing speed into one number, and the sound way to read it is beside the General Ability Index (GAI), never as a verdict on its own. Wechsler publishers introduced it as the counterpart to the GAI, and the ACIS technical manual describes its version as one that "combines working memory and processing speed as cognitive proficiency." An adult can get a normed CPI from a psychologist who gives the WAIS-5, from the ACIS Full Scale form (50 dollars, about 175 minutes) or from the ACIS Custom Test with its five CPI subtests (25 dollars at 5 dollars each), with prices read October 29, 2026. The decisive limit is that a gap between the GAI and the CPI is not a diagnostic marker by itself, which Pearson's own analysis stated, and that ACIS is an online, unsupervised instrument and not a clinical one.

1 What is the Cognitive Proficiency Index?

The Cognitive Proficiency Index is a summary score that pools the working memory and processing speed subtests of a battery, and it describes how efficiently a person handles information, not how well the person reasons or how much the person knows. Pearson's WISC-IV Technical Report 6, by Weiss and Gabel (2008) and read October 29, 2026, opens by saying the CPI summarizes performance on the WISC-IV working memory and processing speed indices in a single score. It adds that the CPI represents a set of functions whose common element is the proficiency with which a person processes certain types of cognitive information. A Pearson presentation on the Wechsler General Ability Index, copyright 2007 and also read on that date, calls the CPI an optional index score for the WISC-IV and the WAIS-IV, "the counterpart to the GAI," derived from the core working memory and processing speed subtests.

The word "proficiency" is the part that misleads. In everyday English it suggests a skill level, as in language proficiency. In this composite it names the efficiency of processing: how quickly and accurately simple information is handled and how well it is held and controlled in mind. The ACIS technical manual, read the same day, lists the CPI in its composite glossary as "working memory and processing speed efficiency" and describes the composite in the sentence quoted above. The definition used in the ACIS report says the same thing in other words: an efficiency and controlled attention profile, not a broad reasoning score.

Three clarifications keep the term from drifting. First, the CPI is a score computed from tests, not a test you take; no one sits a "CPI test," and what differs between publishers is which subtests are pooled. Second, it is a composite beside the primary indices rather than a replacement for them. The page on working memory and the page on processing speed cover the two indices that sit under it. Third, on the Wechsler scales it is optional, computed in addition to the Full Scale IQ and not as a part of it.

Saklofske and colleagues, in a 2010 article in the Canadian Journal of School Psychology that supplied the Canadian norm tables, describe the CPI as reflecting the proficiency and efficiency of cognitive processing and as providing another lens on a child's abilities. The phrase "another lens" is a fair summary: the CPI claims no hidden ability, only a second, narrower view of the same performance, built from the tasks the GAI leaves out. The page on what IQ measures places this view within the larger picture of general ability and its parts.

2 Where does the Cognitive Proficiency Index come from?

The CPI grew out of school psychology, as the second half of a pair with the General Ability Index, and much of the research read for this page was done on children, which limits what can be carried over to adults. Bremner, McTaggart, Saklofske and Janzen, writing in the Canadian Journal of School Psychology in 2011, give the lineage. The GAI was first described for the WISC-III by Prifitera, Weiss and Saklofske in 1998 and for the WAIS-III by Tulsky, Saklofske, Wilkins and Weiss in 2001. Dumont and Willis had earlier proposed a further composite, which Weiss, Saklofske, Schwartz, Prifitera and Courville renamed the CPI in 2006 for use with the WISC-IV, and which was then described for the WAIS-IV as well.

The reason for the pair was practical. Bremner and colleagues explain that the GAI was developed for ability and achievement comparisons when children are assessed for learning disorders. A learning disorder can affect cognitive processing and so pull down the Full Scale IQ, which would shrink the gap between ability and achievement and could limit a child's access to help. Removing working memory and processing speed from the ability estimate was meant to address that. The CPI then reports what the GAI sets aside, so that the information is shown rather than discarded.

The rationale for the CPI itself, in the Technical Report 6 wording, is that proficient processing, "through quick visual speed and good mental control," facilitates fluid reasoning and the acquisition of new material by reducing the cognitive demands of novel or higher order tasks. The report credits the idea of "freeing up" cognitive resources to Weiss, Saklofske, Prifitera and Holdnack (2006), the authors of the book WISC-IV Advanced Clinical Interpretation. That book was not opened for this page. The Pearson report that summarizes it was.

The adult line is more recent. The Pearson WAIS-5 product page, read October 29, 2026, lists the test as published in 2024 for ages 16:0 to 90:11 and names "cognitive proficiency" among fourteen new ancillary index scores. Pearson's WAIS-5 overview brochure, read on the same date, files the GAI and the CPI together under summary index scores. Pearson's guide to the WAIS-5 ancillary index scores, read on that date, lists the CPI subtests as Digit Sequencing, Running Digits, Coding and Symbol Search. The WISC-V page on the same site likewise lists the CPI with the GAI as ancillary index scores and describes it as an estimate of the efficiency with which cognitive information is processed.

One detail on the WAIS-5 page deserves attention. In its answer to a question about which ancillary indices can be used when comparing IQ with achievement, Pearson says every ancillary index is used in either the ability achievement model or the pattern of strengths and weaknesses model, with the exception of the CPI. So even the publisher does not feed the CPI into those two comparison models. That is a reason for caution about how much weight the index can carry as a decision tool, and it returns in the section on what a gap cannot tell you.

3 Which subtests make up the Cognitive Proficiency Index?

The CPI always pools working memory and processing speed subtests, but the exact list changes with the battery, so a CPI from one test is not interchangeable with a CPI from another. The table sets out what the sources read on October 29, 2026 state. The one cell that says "not stated" means the page read did not list the subtests.

The ACIS list has five subtests where the Wechsler editions listed have four. One difference is the memory side: the manual places Visual Sequence in working memory, so the ACIS composite includes a visual span task beside the two auditory ones, and the manual notes that auditory and visual working memory are related but not identical. The other difference is Arithmetic. The Pearson presentation lists Arithmetic as a WAIS-IV working memory subtest feeding the CPI, while ACIS places Arithmetic in its quantitative reasoning index. These are differences of design, and they are why the technical manual is the place to check any composite before comparing it with a number from another battery.

Each ACIS subtest has its own page, and the pages describe formats without disclosing items. The Digit Span page frames the task as immediate auditory verbal storage and, in harder versions, manipulation of ordered material. In the manual the examinee reproduces digit sequences forward, backward and re-ordered into ascending sequence, and a part ends after consecutive errors. The items are presented as audio, so working sound is required. The Alphanumeric Sequencing page describes holding a mixed stream of letters and numbers and reordering each class by a rule, which the manual says separates adequate retention from efficiency once sorting is added. It is also audio. The Visual Sequence page describes holding ordered visual material, and in the manual the examinee watches tiles flash and then clicks them in the order shown and in reverse.

On the speed side, the Coding page describes learning or consulting a symbol key and converting items as fast and accurately as possible. In the manual the examinee works from a key that pairs symbols with numbers under a limit of 120 seconds, each correct match earns a point, and errors are recorded without penalty. The Symbol Search page describes scanning small visual sets and making quick discriminations. In the manual the examinee sees two targets, decides whether either appears in a search array, and has 120 seconds, with incorrect responses penalized, so the subtest measures speed under an accuracy constraint. In CHC terms the first three subtests belong to working memory (Gwm) and the last two to processing speed (Gs), and the page on the CHC model lists the broad and narrow abilities behind those labels.

4 Why combine working memory and processing speed?

The combination rests on the idea that speed and mental control work together, so that slow processing makes every demanding task heavier, but the two abilities stay distinct and the pooled score is a convenience of reporting, not proof of a single faculty. The Technical Report 6 argument has a clear logic. If simple operations run quickly and information is held and controlled well, fewer mental resources are used on the basics, and more are free for the task that matters. Bremner and colleagues restate it in plainer terms: slow processing requires more mental effort, which makes tasks more time consuming and more tiring, and working memory helps reasoning by letting a person integrate new information with what is already known.

Developmental and aging research gives that logic some support, within limits. Fry and Hale, in a 1996 paper in Psychological Science, tested 214 children, adolescents and young adults aged 7 to 19. Their path analyses showed that almost half of the age related increase in fluid intelligence was mediated by developmental changes in processing speed and working memory, and that nearly three fourths of the improvement in working memory was mediated by changes in speed. Even with age controlled, individual differences in speed had a direct effect on working memory capacity, which in turn was a direct determinant of fluid intelligence. The word "mediated" is statistical. This was a cross-sectional design, so it shows a pattern of dependence among the three abilities, not a measured causal chain inside any one person.

For adults, Salthouse's 1996 paper in Psychological Review proposed that age related slowing impairs cognition through two mechanisms. In the limited time mechanism, relevant operations cannot be completed in the time available. In the simultaneity mechanism, the products of early processing may be gone before later processing finishes. The abstract reports considerable shared age related variance across speed measures and a large reduction in the age effects on other cognitive measures once speed is statistically controlled, both consistent with the theory. Neither study validates the CPI as a score. They explain why a composite of memory and speed is plausible as a view of efficiency.

The counterargument is that the CHC model treats working memory capacity (Gwm) and processing speed (Gs) as separate broad abilities, and the ACIS manual defines them separately. Gwm is the capacity to maintain and manipulate information over short intervals under attentional control, and Gs is the speed and efficiency of simple cognitive operations. The manual says working memory and processing speed form a cognitive proficiency cluster but remain clearly distinct, which is why ACIS reports the WMI and the PSI on their own as well. Pearson's presentation makes the same kind of point from the Wechsler side: abilities are interrelated, and even measures of a "pure" domain are not pure. Our reading is that the CPI is best treated as a summary view of efficiency, useful when the two parts agree and less informative when they differ, in which case the separate pages on working memory tests and processing speed tests are the better guide.

The manual adds a rule that guards against misuse: its advanced composites target narrower questions with predefined subtest sets, and it names creating new composites after seeing the profile as a mistake. A composite assembled afterward, from whichever subtests happened to be high or low, answers whatever the person wants. The CPI is the predefined kind, with subtests fixed before anyone sees a result.

5 How is a Cognitive Proficiency Index score read?

A CPI is read like any other composite: it is a standard score with a mean of 100 and a standard deviation of 15, ranked against people of the same age, and how far to trust it depends on how many subtests feed it and how precisely they are measured. The ACIS report places indices on that standard scale and gives a percentile and a 95 percent confidence interval, and the WAIS-5 norms cover ages 16:0 to 90:11 while the ACIS adult norms cover ages 16 to 90. The page on the standard deviation of 15 explains why that scale was chosen. As a worked example, a CPI of 115 sits one standard deviation above the mean, which on a normal curve is about the 84th percentile (our arithmetic on the normal curve, not a figure from any test manual). The page on IQ scores versus percentiles explains why the two must not be averaged or swapped, and the page on how IQ scores are normed explains what the reference group is.

A percentile is a rank and not a frequency: the 84th percentile means the score is higher than that share of the reference group, not that 84 percent of people share it. Because the reference group is age matched, a CPI of 100 at 25 and a CPI of 100 at 65 describe different raw performance, a point a later section develops.

Precision is the second half of reading any score. The Standards for Educational and Psychological Testing (AERA, APA and NCME, 2014), in the open access edition read October 29, 2026, are direct on composites. Standard 2.3 says that for each total score, subscore or combination of scores that is to be interpreted, estimates of reliability or precision should be reported, and its comment adds that composites formed from selected subtests are frequently proposed for predictive and diagnostic purposes, so users need information about the reliability of such composites. Standard 1.14 says that where composite scores are developed, the basis and rationale for arriving at them should be given. Both standards put the burden on the publisher and give the reader a question to ask: where is the evidence for this particular composite?

For ACIS that evidence sits in the technical manual, which lists the CPI with its subtest set and documents its precision. This page quotes none of those statistics. What a reader can do without them is use the confidence interval printed in the report: a CPI is a band, not a point, and a difference between two bands that overlap heavily is weak evidence of a real difference. Five subtests also give the CPI a narrower base than the Full Scale IQ, which draws on all twenty. The page on reliability and validity explains in plain language why a score built from fewer tasks calls for more caution.

6 How does the CPI pair with the General Ability Index?

The GAI and the CPI split a battery in two, reasoning and knowledge on one side and working memory and speed on the other, and the Full Scale IQ sits across both. The live page on the General Ability Index owns the GAI, including its history and its uses, so this section covers only what the pairing adds. Pearson's presentation defines the GAI as derived from the core Verbal Comprehension and Perceptual Reasoning subtests, with reduced emphasis on working memory and processing speed relative to the Full Scale IQ, and the CPI as its counterpart. The same presentation corrects a common myth: the GAI is not the Full Scale IQ with working memory and processing speed removed, because it still taps them to a lesser degree.

On the WAIS-5, the product page's FAQ says the GAI uses the same subtests as the Full Scale IQ minus those that contribute to the working memory and processing speed indices. On ACIS, the GAI page states that the GAI draws on 15 subtests and that the Full Scale form reports a CPI built from the five it leaves out, and 15 plus 5 is the 20 subtests of the battery (our arithmetic). The two Wechsler indices that feed the GAI have sibling pages here: the Verbal Comprehension Index and the Perceptual Reasoning Index.

Reading the pair means asking three questions in order. Do the two differ by more than their uncertainty allows? Is a difference of that size common, which the next section addresses? And does the rest of the profile make sense of it? The manual's own selection rule helps: if the question is reasoning and knowledge without emphasis on speed or working memory, use the GAI; if the question is cognitive efficiency, use the CPI; if the question is broad standing, use the Full Scale IQ. Each answers a different question.

The pair also has a limit. Both composites come from one sitting, so fatigue, motivation and test conditions can move both of them at once. A strong reasoning performance and a weaker speed performance are already visible in the individual subtests and indices, and the composites compress them. The page on the IQ profile test shows how to read a whole profile and when a weak score is noise, which is usually the better first step before any composite comparison.

7 What does a GAI to CPI gap mean in base rate terms?

A gap between the GAI and the CPI has to pass two separate tests before it deserves attention, whether it exceeds measurement error and whether it is uncommon, and the published evidence shows that a single gap often fails the second test. The page on how often index scores differ owns the general method, including why comparing many pairs of scores makes some large gap easy to find. This section applies it to the one pair that matters here, using the numbers that Pearson and independent authors have published.

The first test is statistical. Bremner and colleagues, using the Canadian WISC-IV norm tables of Saklofske and colleagues, report that a GAI to CPI difference of 7.42 points is significant at the .15 level and one of 10.09 points at the .05 level. Those values belong to that edition and those norms, so they show an order of magnitude and are not a threshold for any other test.

The second test is the base rate: how many people in the reference group show a difference at least as big. A gap can pass the first test and fail the second, because a gap can be real and still be ordinary. Bremner and colleagues compared GAI and CPI in small samples of referred children and wrote that, with the exception of the high ability sample, the base rate data do not show that the differences between the two scores are especially uncommon. In their high ability sample of 17 children (those with a Full Scale IQ or GAI of 120 or more), the mean GAI minus CPI difference was 16.00 points, and the base rate attached to a difference of that size was 12.5 percent. That is a finding about a group of 17 referred children, and it describes no individual adult.

Pearson's Technical Report 6 shows how the combination of gaps changes the picture. In that study a "large" discrepancy was defined as 15 or more points, and only the hypothesized direction was counted (achievement below GAI, and CPI below GAI). Among 516 nonclinical children given both the WISC-IV and the WIAT-II, 21 percent had a large ability to achievement difference but no difference between GAI and CPI, which shows that low achievement has many causes and a large achievement gap alone is common. In the other direction, 9 percent of nonclinical subjects with a CPI below the GAI showed no ability to achievement discrepancy. And only 2 percent of children in the comparison sample had both a large CPI to GAI difference and a large achievement to GAI difference, while 45 to 50 percent of the children receiving services in the reading and writing disorder samples met both criteria.

The lesson is about frequency. The report says an achievement gap alone cannot be used as a diagnostic marker, and the pairing of two gaps was rare among children in the comparison sample. These are findings from the WISC-IV standardization project on children, presented as support for a pattern based approach that sits beside other evidence, not as a rule for adults.

Two cautions apply to any reader trying to use these figures. First, the Standards say (Standard 2.4) that when a score interpretation emphasizes differences between two observed scores of an individual, reliability and precision data, including standard errors, should be provided for those differences, and the comment adds that when interpretation centers on the peaks and valleys of a profile, the reliability of score differences is critical. A difference score can be much less reliable than either of the scores it is built from. Second, this page quotes no base rate for the ACIS GAI to CPI gap. The technical manual is where ACIS documents what it has for each composite, and a reader who wants to judge a gap in an ACIS report should read the interval for each composite there before the point difference.

8 What can a CPI gap not tell you, including about ADHD or twice exceptional readers?

A CPI that sits below the GAI is not a diagnosis, a screening result or a sign that something is wrong, and no study read for this page found the gap accurate enough to serve as a marker on its own. This page does not screen for ADHD, learning disorders or any other condition, and an online test cannot confirm or rule one out. The sections below summarize what group studies found, and a group finding never describes the person reading it.

Pearson's Technical Report 6 tested the CPI to GAI discrepancy against 12 clinical groups, each matched to nonclinical controls, with 60 percent as the minimum acceptable sensitivity and specificity. Only four groups cleared that bar. Children receiving services for reading and writing learning disabilities were identified with sensitivity of 66 percent and specificity of 63 percent when the CPI was 5 or more points below the GAI. Closed head and open head traumatic brain injury groups had sensitivity of 65 and 67 percent and specificity of 61 and 62 percent at 4 or more points. A group labeled Asperger's disorder in the report had sensitivity of 68 percent and specificity of 63 percent at 11 or more points. The report's conclusion is that CPI below GAI discrepancies alone cannot be considered a diagnostic marker of any specific learning or clinical disorder, though they are implicated in a variety of disorders and conditions. In our arithmetic on the first figure, a sensitivity of 66 percent means about a third of the children in that group were missed, and a specificity of 63 percent means that about 37 percent of controls were flagged.

ADHD has its own test. Devena and Watkins, in the Journal of Applied School Psychology in 2012, examined whether the GAI to CPI discrepancy could serve as a diagnostic marker of ADHD in samples of 78 and 196 children with ADHD and comparison groups. The area under the curve, where .50 is chance, ranged from .46 to .64 across four comparisons, and the authors concluded that the discrepancy method has low accuracy in identifying children with ADHD. An adult study points the same way. Ryan and colleagues, in Applied Neuropsychology: Adult, found GAI above CPI in 61.9 percent of 42 multiple sclerosis protocols and 78.7 percent of 47 traumatic brain injury protocols, which means the pattern is not specific to one condition, and the area under the curve for separating the two groups was .67, which the authors called low accuracy. The page on IQ tests for adults with ADHD covers what working memory and processing speed findings in adults do and do not support.

Giftedness and twice exceptionality add a different caution. Bremner and colleagues note that research has suggested intellectually gifted children tend to score higher on the GAI subtests and slightly lower on the CPI subtests. They cite other authors for two possible explanations, that gifted children may exert less effort on simple tasks and that reflective or perfectionist styles can slow timed work, and they present these as possibilities and not as findings of their own. A twice exceptional person, someone who combines high ability with a learning or attention difference, may have a profile with a CPI well below the GAI for several different reasons, and a single online score cannot tell which. The page on the twice exceptional test for adults explains what a score hides in that case, and the page on gifted testing for adults covers where the high end of ability is measured.

Even in an adult clinical setting the CPI has not been settled as a tool. Rolin and colleagues, in a 2021 paper in Applied Neuropsychology: Adult, studied 329 adults in an outpatient rehabilitation setting and found that the WAIS-IV CPI added to the GAI in predicting performance on other neuropsychological measures; they wrote that it warrants further study as a clinical addition. Pearson itself, in the WAIS-5 FAQ, leaves the CPI out of its two comparison models. The practical rule, in our reading of these sources, is that the discrepancy belongs in a report beside everything else, not in place of it. If you have concerns about attention, learning or any other condition, the useful step is an evaluation by a qualified clinician, who can use a CPI as one input among many.

9 Does the Cognitive Proficiency Index change with age?

Speed and working memory tasks tend to peak earlier than vocabulary, but the age of the peak depends on the task and the sample, so a CPI should always be read against an age matched reference group. Hartshorne and Germine, in a 2015 paper in Psychological Science, combined 48,537 online participants with an analysis of normative data from standardized IQ and memory tests. Their abstract reports considerable heterogeneity: some abilities peak and begin to decline around high school graduation, some plateau in early adulthood and decline from the 30s, and others do not peak until the 40s or later.

The paper's task level detail matters for the CPI because its parts are the early peaking ones. In the WAIS-III normative sample of 2,450 healthy, cognitively unimpaired Americans aged 16 to 89, three tasks compared in the first experiment peaked, in order, in the late teens (digit symbol coding, a speed task), the early twenties (digit span, a working memory task) and around age 50 (vocabulary). In the authors' second experiment, a web based study of 10,394 visitors aged 10 to 69, two working memory tasks peaked at around age 30, significantly later than processing speed. Both datasets were cross-sectional, so the patterns mix aging with differences between generations, and the authors list that as a limit.

For a reader, three points follow. A raw performance on Coding, Symbol Search, Digit Span or Alphanumeric Sequencing says little by itself, because it is only interpretable against people of the same age. The norm tables of a good test do that comparison for you, which is why a CPI of 100 means average for your age group and not average for adults in general. And because the score is age normed, a steady standing is compatible with changing raw performance, a contrast the page on IQ tests for adults over 40 draws between vocabulary and processing speed. None of this supports reading a low CPI as decline in any individual, because a single administration does not show change.

10 How can an adult get a normed Cognitive Proficiency Index?

An adult can get a normed CPI from a psychologist giving a current Wechsler scale or from a normed online battery that reports it, and free quizzes and brain training apps do not produce one. The table compares the options. ACIS prices and times were read on October 29, 2026 and can change. Cells that say "not stated" mean the source read gave no figure.

The clinician route is the reference for any question with consequences, such as an accommodation or a clinical question, because a professional can observe the session, check effort and put the scores in context. The kit price is what the professional pays, and the fee for an assessment is set by the clinician. Anyone with an existing WAIS-IV report should ask whether the optional CPI was computed.

Free tools answer a different question. A single memory game or reaction time test returns a count or a label for one task, with no norm group or interval in most cases, and it cannot be pooled into a composite. The page on free IQ tests explains what a free result can and cannot support. The ACIS Custom Test is the cheapest normed route to the composite itself: five subtests at 5 dollars each, our arithmetic on the posted price, return the working memory and processing speed domains and the CPI, because "any domain you complete returns its full index score" in the form's own wording and the CPI is built only from those five. 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, which also reports the Full Scale IQ and the GAI that the CPI is meant to be read against.

ACIS is a seller in this market, so treat this section as a disclosure. 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 this composite. A reader who wants a first look at several abilities at once can start from the page on the cognitive ability test.

11 What does an unsupervised CPI session need, and what does the ACIS report show?

Speed and memory tasks are among the most sensitive to the conditions around the test, so an unsupervised CPI needs working sound, a responsive device and a rested session, and the result should be read with those conditions in mind. The ACIS technical manual, read October 29, 2026, says that speeded tasks can be affected by input latency, screen size, visual clarity, distraction, fatigue and motivation, and that working memory tasks can be affected by audio conditions, attention and rehearsal strategy. It adds that online administration requires transparent limits and careful interpretation, and that the right conclusion is not that online testing is unusable. The Standards for Educational and Psychological Testing say the same from the measurement side. In the comment to Standard 3.4 they state that examinees working on older, slower equipment may be unfairly disadvantaged, that devices differing in speed of processing or in the fidelity of visuals can let construct-irrelevant factors influence performance, and that results from unproctored administrations, where standardization cannot be ensured, should be interpreted with caution.

For the five CPI subtests the practical conditions are concrete. Digit Span and Alphanumeric Sequencing present their items as audio and need working sound, so headphones and a quiet room matter more here than on most of the battery. Visual Sequence uses visual tiles and clicks. Coding and Symbol Search are timed, and the manual describes responses made with on-screen buttons or clicks, so a stable connection and a responsive device protect the speed score. The manual does not state which input device is preferable, and this page does not either. Breaks are allowed, progress is saved between subtests and a buyer has 30 days to finish, so the two speed subtests and the two audio subtests can each be taken when fresh instead of at the end of a long session. Fatigue is on the manual's list of influences on speeded work, and rest is the one condition fully within the test taker's control.

The report side is simpler. In the Full Scale form the CPI appears among the composites, and the definition the report uses reads, in substance, that it is working memory combined with processing speed, built from the five subtests named above, and an efficiency and controlled attention profile and not a broad reasoning score. Every subtest returns a scaled score, and the form reports a Full Scale IQ with its 95 percent confidence interval. The Custom Test lets a buyer pick any subtests, returns a full index for any domain completed and returns the CPI when all five of its subtests are bought; the Full Scale IQ itself needs the Full Scale battery. The free trial needs no card and is limited to one per person, and finished trial subtests are kept if the person later unlocks a form that includes them. The example report at the Full Scale link lets a reader see the layout of the report before any purchase.

One point of reading deserves emphasis. The manual lists as a misuse treating a composite as interchangeable with the Full Scale IQ when the construct is different, and it frames the CPI's job as the cognitive efficiency question. A low CPI beside a high GAI describes one pattern in one sitting; it does not say why the pattern exists or that it is permanent.

12 Where ACIS sits, and what a buyer should do

ACIS offers a normed, predefined CPI at a low price, online and unsupervised, which makes it a reasonable way to look at working memory and processing speed together and the wrong tool for any decision that depends on a clinical judgment. ACIS is a seller in this market, so treat this section as a disclosure and check it against the rest of the page. The strengths are specific. The CPI is a predefined composite of five named subtests, defined in advance and documented in the technical manual, scored against adult norms for ages 16 to 90, and reported on the standard scale with a percentile and a 95 percent confidence interval. It includes a visual working memory task beside two auditory ones, and the Custom Test makes it available for 25 dollars (prices read October 29, 2026 and subject to change).

The limits are as important. ACIS is online and unsupervised, so no one observes effort, distraction or device problems. It is not a clinical or diagnostic instrument, and it is not for hiring, school accommodations or admission to high IQ societies. It is English only. Quick and Optimized do not report a CPI, and the manual's form matrix lists it for the Full Scale form alone. This page quotes no ACIS statistic, because the right place to check how precisely each composite is estimated is the technical manual, and a reader who needs that precision for a decision should read it there before relying on any gap.

The Standards for Educational and Psychological Testing (AERA, APA and NCME, 2014), which the American Psychological Association co-publishes, set the benchmark for how a score of this kind should be read, and this page applies five of them. Standard 1.14 asks that where composites are developed, the basis and rationale be given, and that evidence for interpreting score differences or profiles be provided, because evidence for two separate scores does not by itself justify interpreting the difference between them. Standard 2.3 asks for reliability or precision estimates for each combination of scores to be interpreted, and Standard 2.4 asks for such data on the differences themselves. Standard 5.1 says test users should be given clear explanations of the characteristics, meaning and intended interpretation of scale scores and their limitations, and Standard 6.10 asks that interpretations describe in simple language what the test covers, what scores represent, the precision of the scores and how they are intended to be used. The introduction to the Standards' chapter on psychological testing and assessment adds that the interpreter of results should be informed if a test was unproctored. Read this way, an online CPI is informative about a person's performance on five tasks in one sitting, and it becomes a basis for a judgment about attention, learning or ability only when a qualified professional puts it with other evidence.

A buyer can act on that in order. Decide first whether the question is about efficiency or about reasoning, because the CPI answers only the first. If the question carries consequences, start with a clinician and ask which indices were computed, including whether the optional CPI was. If the question is personal curiosity, take the Full Scale form for the full picture, including the GAI beside the CPI, or the Custom Test with the five CPI subtests for the composite alone. Use working sound, a responsive device and a quiet room, read the CPI beside the GAI and the Full Scale IQ with their intervals, and treat any gap as a prompt to look at the individual subtests, not as a conclusion. The cheapest concrete next step is the free trial, which needs no card.

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. Our own arithmetic is labeled as such in the text. Pages were read on October 29, 2026, and prices on those pages can change.

• Weiss L G and Gabel A D. Technical Report #6: Using the Cognitive Proficiency Index in Psychoeducational Assessment. Pearson WISC-IV technical report, 2008.
• Bremner D, McTaggart B, Saklofske D and Janzen T. WISC-IV GAI and CPI in Psychoeducational Assessment. Canadian Journal of School Psychology, 2011, volume 26, issue 3, pages 209 to 219.
• Saklofske D, Zhu J, Coalson D, Raiford S and Weiss L. Cognitive Proficiency Index for the Canadian Edition of the Wechsler Intelligence Scale for Children-Fourth Edition. Canadian Journal of School Psychology, 2010, volume 25, issue 3, pages 277 to 286.
• Zhu J, Raiford S E and Coalson D, with discussant Saklofske D. The What, When, and How of the Wechsler General Ability Index. Presentation, Pearson Education, 2007.
• Pearson. Wechsler Adult Intelligence Scale, Fifth Edition (WAIS-5) product page. Publication date 2024, read October 29, 2026.
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14 Frequently Asked Questions