You can detect a lot about a person using simple tasks which take less than 2 minutes. Here is a test which did the job in 90 seconds, but then got lengthened to 120 seconds to make it even more reliable. Of this test, one of those Edinburgh researchers said to me in a conference coffee break: “it is better than a brain scan”. What did he mean?
In order to get an overall estimate of mental power, psychologists have chosen a series of tasks to represent some of the basic elements of problem solving. The selection is based on looking at the sorts of problems people have to solve in everyday life, with particular attention to learning at school and then taking up occupations with varying intellectual demands. Those tasks vary somewhat, though they have a core in common.
Most tests include Vocabulary, examples: either asking for the definition of words of increasing rarity; or the names of pictured objects or activities; or the synonyms or antonyms of words.
Most tests include Reasoning, examples: either determining which pattern best completes the missing cell in a matrix (like Raven’s Matrices); or putting in the word which completes a sequence; or finding the odd word out in a series.
Most tests include visualization of shapes, examples: determining the correspondence between a 3-D figure and alternative 2-D figures; determining the pattern of holes that would result from a sequence of folds and a punch through folded paper; determining which combinations of shapes are needed to fill a larger shape.
Most tests include episodic memory, examples: number of idea units recalled across two or three stories; number of words recalled from across 1 to 4 trials of a repeated word list; number of words recalled when presented with a stimulus term in a paired-associate learning task.
Most tests include a rather simple set of basic tasks called Processing Skills. They are rather humdrum activities, like checking for errors, applying simple codes, and checking for similarities or differences in word strings or line patterns. They may seem low grade, but they are necessary when we try to organise ourselves to carry out planned activities. They tend to decline with age, leading to patchy, unreliable performance, and a tendency to muddled and even harmful errors. When we lose our ability to do even simple tasks, then the care home beckons.
One of these simple tasks is called Coding. It is also known as Digit-Symbol. You are shown a code box in which every number from 0 to 9 has a symbol underneath. Your task is to go through a whole set of numbers, each with an empty box underneath, and fill in the appropriate code. So, you look at the first number in the sequence, look up at the code box to find the appropriate code for that number, and then draw it in to the box. It is a dull task, like being a university teacher.
First, here is the overall picture which comes from Salthouse’s review of the data on ageing.
Localizing age-related individual differences in a hierarchical structure. Timothy A. Salthouse. Intelligence 32 (2004) 541–561
Data from 33 separate studies were combined to create an aggregate data set consisting of 16 cognitive variables and 6832 different individuals who ranged between 18 and 95 years of age. Analyses were conducted to determine where in a hierarchical structure of cognitive abilities individual differences associated with age, gender, education, and self-reported health could be localized. The results indicated that each type of individual difference characteristic exhibited a different pattern of influences within the hierarchical structure, and that aging was associated with four statistically distinct influences; negative influences on a second-order common factor and on first-order speed and memory factors, and a positive influence on a first-order vocabulary factor.
Personally, I am glad to see that Vocabulary holds up, but the rest fall sharply with age. To my eye the fall in perceptual speed is sharp, linear and with a pronounce slope. It plunges in a straight line. Here are the Wechsler standardisation data, and the overall findings from the meta-analysis.
This is what the task looks like.
Digit Symbol is such a simple task, almost free of any intellectual content, that it almost seems a measure of the brain’s clock speed, a clear indicator that old brains work more slowly than young ones. Given this finding, it is understandable that the coding task is a good predictor of how the person is ageing, and how well they are able to cope with the problems of everyday life. A brain scan, for all its apparent precision, is not a direct measure of actual performance. Currently, scans are not as accurate in predicting behaviour as is a simple test of behaviour. This is a simple but crucial point: so long as you are willing to conduct actual tests, you can get a good understanding of a person’s capacities even on a very brief examination of their performance.
The Digit Symbol test indicates current functioning. It does not assess previous levels of ability as is the case with the Adult Reading Test. (By the way, this test is absolutely nothing to do with regional accents. It is a test of whether you have learned how a specific set of irregularly written words are pronounced. For example, the word “Ache” has one pronunciation according to the usual rules of English, and another according to the quirky way in which English is written.
Exactly where Digit Symbol comes in the hierarchy of abilities is not my concern here. I just want to explain that much maligned “paper and pencil” tests (and their computer and keyboard equivalents) can be very powerful indicators of important personal abilities, with very profound consequences.
There are several tests which have the benefit of being quick to administer and powerful in their predictions. Digit Symbol is useful because it is a ratio scale. Each additional symbol the person puts in adds directly to their raw score. Another good, and even quicker test is Trail Making B which has a strong loading on g and also on an orthogonal processing speed factor.
All these tests are good at picking up illness related cognitive changes, as in diabetes. (Intelligence testing is rarely criticized when used in medical settings). Delayed memory and working memory are both affected during diabetic crises. Digit Symbol is reduced during hypoglycaemia, as are Digits Backwards. Digit Symbol is very good at showing general cognitive changes from age 70 to 76. Again, although this is a limited time period in the elderly, the decline in speed is a notable feature.
Predictors of ageing-related decline across multiple cognitive functions.
Stuart J. Ritchie, Elliot M. Tucker-Drob, Simon R. Cox, Janie Corley, Dominika Dykiert,Paul Redmond, Alison Pattie, Adele M. Taylor, Ruth Sibbett, John M. Starr, Ian J. Deary.
Intelligence 59 (2016) 115–126.
A few words about ageing: it all goes together when it goes. Or, at least 48% of the decline is shared across the board. The general tendency for most people is that brighter children become brighter, healthier, and fitter older adults. This ‘preserved differentiation’ appears to last into the eighth decade of life.
There is a fly in the ointment: The most robust and consistent predictor of cognitive change within old age, even after control for all the other variables, was the presence of the APOE e4 allele. APOE e4 carriers showed over half a standard deviation more general cognitive decline compared to noncarriers, with particularly pronounced decline in their Speed and numerically smaller, but still significant, declines in their verbal memory.
It is rare to have a big effect from one gene. Few people carry it, and it is not good to have. Perhaps in future people will try to delete it. However, I would suggest caution, because it might conceivably be useful in other contexts.
There is more detailed work on these simple tests, but they make an important point: a well-designed simple test can improve decision-making. Digit Symbol isn’t the best test of general intelligence, but it is very good at detecting health problems and ageing. Originally it was seen as the key test (I still hold on to this because of the simplicity, and the enormous number of times it has been given in clinical practice) but it is now seen as one of a number of processing speed tasks.
In brief, brief tests identify real-life changes, with important consequences.