Are Emotive Appeals Effective in Persuading People to Give to Charity?

In today's media-heavy world, in which people are bombarded by ads and asks multiple times every day, charities are frequently told that if they want to attract attention to their causes and raise money they need to create emotive appeals. However, at the same time, charities are often warned against using guilt as a way of encouraging people to give.

But just how effective are emotive appeals of any kind? And how can charities ensure they are carefully balancing emotion without falling into guilt-tripping?