The Joshua Greene and Lucius Caviola article about their givingmultiplier.org work has just been published. Here's the abstract:

The most effective charities are hundreds of times more impactful than typical charities. However, most donors favor charities with personal/emotional appeal over effectiveness. We gave donors the option to split their donations between their personal favorite charity and an expert-recommended highly effective charity. This bundling technique increased donors’ impact without undermining their altruistic motivation, boosting effective donations by 76%. An additional boost of 55% was achieved by offering matching donations with increasing rates for allocating more to the highly effective charity. We show further that matching funds can be provided by donors focused on effectiveness through a self-sustaining process of micromatching. We applied these techniques in a new online donation platform (GivingMultiplier.org), which fundraised more than $1.5 million in its first 14 months. While prior applied research on altruism has focused on the quantity of giving, the present results demonstrate the value of focusing on the effectiveness of altruistic behavior.