Now that we have some British politicians talking about IQ it seems the right time to rush out a summary I was slowly preparing about the lives and achievements of different intelligence bands. Please accept this as a general overview, subject to revision, to which more illustrative details and precise boundaries will be added at a later date.

Tribe 1 “High Risk”

These are the least able 5% of the population. In a town of 10,000 persons these would constitute 500 citizens. Learning is slow, so all intellectual achievements take a fair bit of time. Since all lifespans are finite, and for this group lifespans are shorter than average, many skills are effectively out of reach because it is very unlikely that they will ever be learnt. Of course, some learning always takes place, because everyone can learn, but in their case the pace must be slow, the materials simple, and the steps carefully supervised.

Lifespans are more than 21% shorter than average, and they are more than 50% more likely to be suffering psychological difficulties than average. They are most at risk of all health problems, and all the problems of life.

These people are “high risk” because they make unforced errors and because they are at risk of being exploited by the unscrupulous. They are less likely to follow rules (perhaps they cannot see the point of them) or to delay gratification, and more often than average to wind up in trouble. They have high levels of credulity, tend to believe in god and magic and coincidence and miracles. Vocabularies are relatively mall, not much above the functional basics of the language. As a rule of thumb, if you understand the 3000 most frequent English words then you will understand 95% of the words in common use. If you understand 5000 words (and their close variants) you get 99.9% word coverage in ordinary language. Computations are restricted to simple operations, mostly addition and subtraction.

They can sign their name and add up the total of bank deposit entries. They can do basic concrete tasks. In terms of reading and entertainments they like stories, picture magazines, music with strong melodies and rhythms, and broad comedy. (Later we can get into the details about what entertainments and materials are favoured). Employment opportunities, which would have been plentiful in simpler agrarian societies, are now far more limited, tenuous, and precarious. Modern life has become very demanding, and simple physical labour no longer adds much value. Their wages will be low, and in kinder and wealthier societies they are likely to be receiving social benefits. The armed services will not recruit them. They have frequent periods without paid work. They will have no effective savings.

There is little about their appearance which would indicate limited intellectual power, and their social conversation is usually in line with basic social niceties. It would take more somewhat more extensive conversations to reveal shortcomings. They can use mobile phones and drive cars, though they would have difficulty with the driving theory exam. They would also crash about three times more often than average. They are very recognisably our cousins, much more like us than not. In IQ terms they are 75 and below.

Tribe 2 “Uphill Battle”

These are the next 20% of the population in terms of ability. They would be 2,000 citizens in the town of 10,000 inhabitants. Learning is somewhat faster, and achievements are of better quality. Learning varies from the slow pace, simple materials and careful supervision already mentioned previously, to very explicit, hands-on training. They tend to credulity, belief in god and superstition. They can locate the intersection of two streets on a map, identify two features in a newspaper sports story, perhaps calculate the total cost of purchases listed in a catalogue, and draw inferences from two identifiable facts and deal with some distractors.

Vocabularies are somewhat larger, computation includes some multiplication and division. In terms of reading they will enjoy a little more depth in terms of content. Employment opportunities include simple assembly and packaging tasks, food preparation, assistant roles in caring professions. They can use some checklists, and procedural guides. The armed services will probably not recruit them, because many of them will take too long to train.

They have a 21% lower survival up to age 76 (Whalley&Deary 2001). They have about a 50% greater risk of hospitalization for schizophrenia, mood disorder, and alcohol-related disorders (Gale et al. 2010) and for personality disorders (Moran et al. 2009) with more self-reported psychological distress (Gale et al. 2009) and with a greater risk of vascular dementia (McGurn et al. 2008).

They will probably have fast lifestyles, with restricted planning and savings. They have more accidents than average, probably twice as many motor vehicle accidents than average. In IQ terms they are between 75 and 90.

Tribe 3 “Keeping Up”

These are the middle 50% of the population. They are the “average” the “man in street” the person with “common sense”. By definition, this is what most people are like. In our town of 10,000 they would constitute a massive 5,000 persons. The town would be built round them, their abilities, their needs, and their frailties. In the way that clothes are mass produced for average sizes and fashions, the town would be made to their taste. The money would follow them. Films, TV, books, magazines, and newspapers are written for them.

Learning is mostly mastery learning, hands on. The brighter ones learn from written materials plus experience. They can deal with tasks which require the integration of multiple pieces of information from one or more documents, which themselves may be complex and contain much irrelevant information. However, the matches they are asked to search for tend to be literal, and the correct information in the test material is not located near incorrect material, where it would be too confusing.

They are almost always able to calculate the total costs of purchases from an order form; write a brief letter explaining an error made on a credit card bill; and using a calculator, work out what the discount would be on a bill if paid within 10 days; enter information into a car maintenance record; and perhaps be able to state in writing the argument made in lengthy newspaper article. Vocabularies are in the 17,000 to 21,000 range, with older people in the upper part of the range.

They may believe in god, have some superstitions, be fooled by some coincidences, have difficulty in calculating some odds, but are usually adept at using rules of thumb and avoiding confidence tricks and deceptions. They know that magic depends on tricks, even if they cannot explain them. Their understanding of science will be basic and subject to omissions. They can catch out brighter people in errors, and tend to be pragmatic, with little theory. However, they may believe that day and night are due to the earth going round the sun.

They occupy the middle range occupations, in what used to be clerical trades, and sales jobs of all descriptions. Likely jobs are Police officer, nurse, trainer, and when the job was still available in the economy, machinist. They will delay gratification to some extent, and have some savings. Incredibly, in modern welfare states they would only just be net contributors in tax terms, but would mostly get benefits in almost equal proportion to their tax contributions.

As you would expect, motor vehicle accidents are at the average rate. In IQ terms they are between 90 and 110.