# The Amazon Percentage Trick

Can you spot the numeric trick Amazon is using in the image below? It tricked Techdirt  into saying “books increased between about 4,000% and 6,500%. Yes, that’s multi-thousands of percent increases”.

Amazon have gained masses of PR & links as a result of this simple little trick over the years, and authors (like Paulo Coelho) have benefited from its misleading nature. Gizmodo, The Metro, Huffington Post, The Guardian, The Mirror, and many others all fell for this same trick around the time of the London Riots, reporting a 5,000% rise in Baseball Bat sales.

The trick is that the % numbers are nothing to do with an increase in actual sales. They’re actually a somewhat meaningless number used to describe the increase in ‘Amazon Sales Rank’.

The maths is:

((Old Sales Rank / New Sales Rank) * 100) – 100

So, for example, if we look at number 3 on the list up there, “The Devil & Miss Prym” was in position 9,760 in Amazon’s sales rank (ie there were 9759 books selling more copies). Now it’s at position 202 (there are just 201 books selling more copies). The formula is:

((9760 / 202) * 100) – 100 = 4,731

Amazon report that using an up arrow and ’4,731%’ and we naturally jump to the conclusion that means the book’s unit sales have increased 4,731%. In reality, we still have no idea of the actual change in unit sales.

As a simple example: If we follow the idea of ‘the long tail’, a book at position ’220′ in Amazon’s charts may not sell a whole lot more than a book at position ’9760′. It may simply be that the book sold 30 copies last week (in position 9,760) and sold 60 copies this week (in position 220). That would simply mean a 100% increase in sales, rather than 4,731%.

In fact – though unlikely in this case – it’s possible for products to increase in ‘sales rank’ even when they sell less units.

Amazon use lots of clever pricing, ranking & user interface tricks like this – it’s worth keeping an eye out for others.

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