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As a rule of thumb the longer a coin is sitting in someone's wallet the less likely it is to be spent on emotions. In fact, we've conducted a statistical study revealing that ~139d age mark is a point at which the coin holder's probability of spending reduces dramatically.

The holder behaviour changes so that from around this age mark she can be considered part of a 'smart money' group. There is a +/- 20d gradient around the 139d mark to take into account a smooth transitioning of holders from the STH to the LTH group.