Global Citizen Corps leaders host a fundraiser for World AIDS Day. Photo: jessicaphansen (flickr)

On last year's World AIDS Day, Sam held an afterschool open-mic event to raise awareness of HIV/AIDS. Rachel got 200 people to sign a letter asking for more government attention on AIDS — and sent it to Barack Obama. Lily had a candlelight ceremony in memory of those who have died from the disease.

So who are these youth?

They're all members of the Global Citizen Corps leadership program — a national network of high school students that are committed to ending global poverty.

Global Citizen Corps leaders build awareness in their communities by organizing informative events at their schools that focus on issues like climate change, HIV/AIDS, world hunger, and access to education.

Dozens of teens are making a difference. Jaime wrote an article her high-school newspaper to raise awareness about global poverty. Kate hosted a "blackout" at her school, cutting off the water to show students how climate change can impact people's lives.

Global Citizen Corps is looking for more dedicated and compassionate youth to join the program. Students gain access to Mercy Corps resources and agree to host informative events at their school or in the community. Leaders will also have the opportunity to lobby for access to education in Washington D.C. and participate in the annual leadership summit in New York City.

The 2009-2010 High School Leadership Program is now accepting applications. The deadline is April 15, so apply today.

We hear a lot about people who live on “less than a dollar a day.” But a dollar buys a lot more in some countries than it does in others. That’s why some economists believe a better way of understanding the relative income of people around the world is through something called Purchasing Power Parity.

A simple way of understanding this concept is through the words of BBC Reporter Mukul Devichand, who explains how the “Big Mac Index” — first coined by The Economist — is a good way of understanding price differences between countries.

The idea, says former World Bank economist Michael Ward, is that the Big Mac is an almost identical product no matter where in the world you buy it — bread, cheese, meat, lettuce and labour costs. But in fact, Big Macs end up costing much less in places like Beijing or Mumbai than London or New York.

So economists use the different prices of Big Macs across the world to judge the relative buying power of people in different countries. For example, if a Big Mac costs a dollar in America, but only 25 cents in Mumbai, then a PPP "dollar" in Mumbai is actually worth only 25 cents.

It’s a good idea to keep the dollar’s relative worth in mind when checking out the portfolio of pictures on onedollaroneday.org, sponsored by our sister site Global Citizen Corps. The site is challenging its visitors to submit photos that answer the question, “What can you eat on a dollar a day?”

With Global Citizen Corps’ global audience, it’ll be interesting to see how submissions from the U.S. differ from those from, say, Spain or Syria or Sudan.

Students aged 14-25 can register with Global Citizen Corps and submit their photo on flickr.com. The grand prize is a digital camera, with Amazon.com gift cards for second and third place. The deadline is August 20.