How can you compare helping two different people in different ways?
When people ask what aspiring effective altruists work on, I often start by saying that we do research into how you can help others the most. For example, GiveWell has found that distributing some 600 bed nets, at a cost of $3,000, can prevent one infant dying of malaria. For the same price, they have also found you could deliver 6,000 deworming treatments that work for around a year.
A common question at this point is ‘how can you compare the value of helping these different people in these different ways?’ Even if the numbers are accurate, how could anyone determine which of these two possible donations helps others the most?
I can’t offer a philosophically rigorous answer here, but I can tell you how I personally approach this puzzle. I ask myself the question:
Which would I prefer, if, after making the decision, I were equally likely to become any one of the people affected, and experience their lives as they would? 
Let’s work through this example. First, we’ll make the number of people we are considering a manageable number: for $5, I could offer 10 children deworming treatments, or alternatively offer 1 child a bed-net, which has a 1 in 600 chance of saving their life. To make this decision, I should compare three options:
I don’t donate, and so none of the 11 children receive any help
Ten of the children receive deworming treatment, but the other one goes without a bed-net
The one child receives a bed-net, but the other ten go without deworming
Being ‘fair’, because in theory everyone’s interests are given ‘equal consideration’
Putting the focus on how much the recipients’ value the help, rather than how you feel about it as a donor
Motivating you to actually try to figure out the answer, by putting you in the shoes of the people you are trying to help.
How much would deworming improve my quality of life immediately, and then in the long term?
How harmful is it for an infant to die? How painful is it to suffer from a case of malaria?
What risk of death might I be willing to tolerate to get the long-term health and incomes gains offered by deworming?
And so on.