Where can a dollar improve the most lives? That’s the question guiding GiveWell, a nonprofit that last year directed over $400 million to interventions like malaria medication and lifesaving vitamin A shots.  Elie Hassenfeld co-founded GiveWell at 25. Then working at a hedge fund, he and a colleague, Holden Karnofsky, wanted to donate money but were “shocked by how little useful information was available,” Hassenfeld says. So they quit their jobs to do for charities what they’d done for investors: dig into the numbers.  Founding an organization that implied much of charity was wasteful "pissed a lot of people off," Hassenfeld concedes. "I don't think it was the right tone." True to form, GiveWell—which prides itself on transparency—lists “tone issues” among the errors on its public "Our Mistakes" webpage.  Even so, Hassenfeld can’t help but shoot straight. Over a thousand children die from malaria each day.…