The hidden tax you pay for waiting

IMAGINE that whenever you planned to do volunteer work, the government told you that you must also pay a small tax. Or suppose that whenever you gave money to charity, you were charged a levy. Or that every time you gave blood, you had to start by writing a cheque to the Internal Revenue Service.

Fortunately, most countries don't tax people for good deeds. But private and public institutions do - by taking up too much of people's time. And like all taxes, a "time tax" discourages people from engaging in the particular behaviour that it penalises.

Striking evidence for this comes from a new study by Australian economics professor Robert Slonin. With the help of a large data set from the Australia Red Cross Blood Service, Prof Slonin and his co-authors quantified how variations in waiting time affected the likelihood that blood donors would come back to give again.