The 'serial sevens' task, in which subjects are asked to count backwards from 100 by repeatedly subtracting 7 (e.g. 100-93-86-79-72-etc), is a commonly used test in the assessment of cognition. It is part of the standard set of tasks used to assess people for cognitive decline - the mini mental state examination (or MMSE) and is worth 5 out of the 30 available marks. Attention and memory are required to perform the task.
Dementia is common and rates will increase dramatically in the coming years. There is a strong drive towards earlier detection with a view to earlier treatment - identification of mild cognitive impairment. In parallel, public awareness of dementia or cognitive impairment has increased significantly also. Many people know or have known someone with dementia and many will have attended hospital or general practice appointments with this person. Dementia now receives greater mention in the media, both factual and fictional, than ever before. For these reasons, subjects are increasingly likely to be aware of the mental tests that will be performed if their cognition comes under assessment. The 'serial sevens' test has gained particular notoriety!
In the PREDICT-PD study we use a standard battery of cognitive tests called the Montreal Cognitive Assessment or MoCA, which like the MMSE, includes the 'serial sevens' task. It is not uncommon for our research subjects to say that they were expecting the 'serial sevens' as part of the assessment and consequently have been practising. A practised test uses different memory retrieval processes and significantly less attention; I am certain that practise improves the likelihood of scoring full marks.
Alternatives to 'serial sevens' exist and include: using a number other than seven, naming months of the year in reverse order and spelling WORLD backwards. Each of these are slightly different in terms of difficulty and it is tricky to pool data in a research setting if different tests have been used. On an individual basis, substitution of the 'serial sevens' test for an alternative is often appropriate and may yield findings that were not apparent when a practised 'serial sevens' test was performed. Nonetheless clinicians should be aware that prior knowledge of such tests, particularly ones that can be practised, may mask a subtle decline in cognition when using standardised assessments.
- Alastair Noyce
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