>>e freakonomics broadcast. >> reporter: turns out barbara sine and those like her are key players in a medical revolution, and economics non l laureate alth deserves much of the credit. aers a market e he'd been puzzling over how to increase the number of kidney transants. dialysis keeps patients alive while they wait, usually years, for a deceased donor kidney, or, fif they're lucky, a kidnm a living donor who's a good biological match. and then al rothays he heard about two spouses chatting in the waiting room of a dialysis clinic. >> why are you here? i'm waitg for my husband. i would give him my kidney, but he has blood type b and i have ablood ty oh it's a funny thing my, you know, we're just reverse. >>epter: so the wife with blood type a gave one of her two kidneys, we can live with just one, to the other spouse. and her blood type b husband got a eykirom the person she'd met in the waiting room. but roth saw a way to go beyond two cples swapping two kidneys, by using computer algorithms to create donor- recipient chains, matched for blood and tissue type, even for age. one pr

that's going to be the trophy case now. >> reporter: meanwhile, barbara sine has yet to meet her recipient. >> i know that a man about my age got my kidney and i do know that his wife was scheduled to donate i think the following week. and that's about all i know. or>> rr: would you be more and more happy as a function of whether or not more and more people were in your chain? >> well, yes, i mean, i think tpehe morle who are helped the better. t che idea that help 10, 15, who knows! >> porter: and bottom line, that's what makes this tear- jerker an economics lesson as well. >> well, altruism seems to recond to some of the econo incentives that other goods do. if you can do re good with a dollar, you're more likely to give a second dollar. >> reporter: oka you can't give a second kidney. but you can sure do a world of good ging just one. this is economics correspondent paul solman, reporng from new jersey. >> nawaz: pope francis broke his silence on wednesday acknowledging for the first time that clergymen have sexually abused nuns. john yang has more on the story >> yang: amna, for decade