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Dr Chris Cates' EBM Website

Visual Rx - Examples

Visual Rx Cates Plot Example

The Cates Plot shown above is an example of the output from a Cochrane Review of the use of antibiotics in Acute Otitis Media (middle ear infection) in children. The data is taken from the Cochrane Library 1999 issue 4.

The picture represents 100 children who are all given antibiotics for ear infections. The 86 green faces are children who would have been free from pain at 2 to 7 days even if they had not received an antibiotic. The 9 red faces are children who are still in pain even with antibiotics. The 5 yellow faces are the only children who show a benefit; they would have been in pain without the antibiotic but are not when they receive one.

Since it is not possible to identify which children will benefit all 100 need to be given the antibiotic for 5 to benefit. This represents the number needed to treat (NNT) of 20 for a single child to benefit.   A summary of the NNTs from the updated Cochrane review can be seen in the October Newsletter.

Visual Rx Cates Plot Example

In contrast this Cates Plot shows that when all 100 children are given antibiotics an extra 8 will suffer diarrhoea, vomiting or a rash. This means that the number needed to cause a harmful outcome in one child (NNH) is 13.