December 23, 2014

Homocysteine, Memory Loss And Dementia - Assessing Causation

Association and Causation

In previous blogs we've described the evidence linking high blood levels of homocysteine to memory problems, cognitive decline and dementia - including Alzheimer's Disease.

But how do scientists go from showing a 'link' between conditions and proving causation? 

Sir Austin Bradford Hill

Sir Bradford Hill was Professor Emeritus of Medical Statistics at the University of London.  In 1965 he gave an important talk concerning the relationships between sickness and working conditions.

He considered that, if something is associated with a biological event, how can we say this is causative?

Nine Key Features?

Hill suggested nine features of an association that might help decide if the most likely interpretation is one of causation:

  1. Strength

  2. Consistency

  3. Specificity

  4. Temporality

  5. Biological gradient

  6. Plausibility

  7. Coherence

  8. Analogy

  9. Experiment


None of these bring indisputable evidence for causation.  But they help address whether we can explain an association other than cause and effect.

In the next series of blog updates we will look closely at the link between homocysteine, memory loss and dementia in terms of each of Hill's suggested characteristics.

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