Most people have heard the ‘2.4 children’ argument or a permutation of it. The phrase comes from a time when the average number of children per family was 2.4. The figure made perfect sense as a statistic even though it applied to not one family in the world. Unfortunately, a lot of psychological research falls foul of the same problem: although the results of many studies describe the whole population very well, they do not describe any individual picked at random with any great accuracy.

Of course there are times when psychological research does nail it on the head. For example, within the mainstream population it is a safe bet that anyone you stopped in the street would have a short term memory for seven items plus or minus two (though good luck in stopping someone on the street and getting them to do a short term memory test). It is also a good bet that if you were invited to a funeral in most countries you would wear suitably sombre clothes, because you would wish to conform. There are some psychological laws that apply more or less to all of us.

However, there are other situations in which the general rules just cannot reliably help you on an individual basis. Take for example the topic of dementia. As a professor of psychology, I get the occasional email or letter from a person who has read my work and wants advice on a relative who is showing signs of cognitive decline. My answer is always a blank (though I hope polite) refusal – not out of hard-heartedness, but for two reasons. The first is that I am not a clinical psychologist and my professional body doesn’t take kindly to academic psychologists offering diagnosis and therapy. The second is that in any case, there are just too many variables involved to make an answer that is specific enough to be useful.

For example, suppose that an older person becomes more forgetful. Does this mean they have dementia? Possibly, since all types of dementia involve memory loss. But before we leap to this conclusion, there are a hundred and one other causes that need to be ruled out first. For starters, some memory loss is normal in everybody’s later life. Perhaps the person concerned is showing normal decline, but those around him or her are hypersensitive to any change. Again, a larger decline than average happens in some people – this is enough to be noticeable to an impartial observer, but it is not so large that it is likely to interfere with everyday functioning. This so-called mild cognitive impairment can, it is true, develop into full-blown dementia, but in a significant number of cases, it does not. Again, many apparent memory failings can in fact be due to other, easily remediable causes, such as a decline in hearing (how can you remember something if you never heard it in the first place?).

Furthermore, no two cases of dementia are exactly the same, at least in the early stages. A common misconception is that the first obvious sign of dementia is memory loss. In fact, other symptoms, such as a change in personality or problems doing skilled movements are common (and again, these changes are shared with a host of other conditions and cannot be automatically assumed to indicate dementia). Plus, the previous level of intelligence of the person can distort matters. It has been argued (though some researchers have disputed this) that a set of good cognitive skills will enable an individual to hide (deliberately or accidentally) a considerable degree of loss because the skills that survive are still better than average for quite some time into the illness’s progression. Conversely, someone with a low IQ might show a considerable decline without anyone noticing a significant change, simply because there is a low expectation of what the person is capable of doing.

The above is the tip of the iceberg. There are a lot (and I mean a LOT) more confounding factors that mean that trying to give individual advice is so difficult as to be inadvisable. However, I have not raised this point simply to offer an expanded explanation of why I don’t offer specific advice. I also wanted to illustrate a further, very important point, which is this. When we look at people with dementia, it is very tempting to see the disease and not the person. We are so attuned to the hideous aspects of the condition that we can easily forget that the person with dementia is, until the late stages of the condition, very much aware of at least some aspects of their surroundings, and can still have profound likes and dislikes. The late Tom Kitwood argued that dementia presents itself as the sum of its parts, and these are not just neurological impairment, but also personality, background, health, and general surroundings. Now if you stop and think about this for a moment, if you knock out neurological impairment, that list pretty much describes what makes all of us what we are.

Dementia is not a cut and dried business. We need to stop thinking about it as if a one size fits all explanation will ever suffice, and realise that beyond the illness, a vast range of factors all impinge to make the person with dementia what they are. And those same factors shape the rest of us as well.

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