Glass of carrot juice

Natural causes: carrot juice

Understanding the stats

Q: I just read online about a man who cured his cancer with carrot juice. Why can’t we all use natural remedies?

A: Remember a key saying in statistics: correlation does not equal causation. In other words, just because there is a relationship between the volume of carrot juice the man consumed and the disappearance of his cancer, it doesn’t mean that one caused the other.

Even if it did, think what you’re not hearing about. If he had died in spite of all the carrots, would an article have been written about it? Maybe there are thousands of failures out there that are not being reported. This is an example of ‘selection bias’ – where you only hear about the ‘successes’.

A related phenomenon, ‘publication bias’, happens in scientific research. Journals and some researchers are more likely to publish new, exciting results than ‘negative’ findings that a particular variable does not cause an effect.

Medical science does not work on the basis of anecdotal evidence (based on personal experiences), but through carefully controlled trials.

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Further reading

About this resource

This resource was first published in ‘Number Crunching’ in June 2013.

Statistics and maths, Health, infection and disease
Number Crunching
Education levels:
16–19, Continuing professional development