The viral nature of the #icebucketchallenge guaranteed its success, but herein lies the danger; the viral means of a campaign automatically determine which charities get the most funding, when instead we should consider those that have the most impact.

Tim Harford believes ‘a true nerd doesn’t run with the herd.’ As people across the world poured freezing water over their heads and supported ALS (amyotrophic lateral sclerosis) - or Motor Neurone Disease, he embarked on a quest to find the most deserving cause for his ice bucket challenge. 

After talking to Elie Hassenfeld of Give Well, he used quality-adjusted life-years (QALYs), which combine the quantity and quality of life generated by healthcare interventions into one single measure. This assessment will tell you that choosing to fund worming tablets provides the best bang for your buck.

Between 1.4 and two billion people suffer with parasitic worms, of whom about 210 million suffer from Schistosomiasis according to the World Health Organisation. Worming tablets are a cheap, simple solution to the disease – caused by the parasite migrating to vital organs and causing damage – and numerous other problems. 

Measuring impact by using QALYs can be useful when thinking about where to allocate funds. But it doesn’t tell the whole story. Impact is made up of several dimensions: urgency of need; effectiveness of response (efficacy of intervention combined with the ability of organisations to deliver the intervention); and in some but not all instances, the cost benefit of response. 

So here are the problems with Tim’s ice bucket decision:

By taking a purely cost – bang for your buck – approach, you risk discriminating against anything that is expensive to fix. Many human miseries are complex to solve, and cannot be reduced to the simplicity of one worming tablet. Are you only going to fund things that are simple and cheap to deliver?

The number of QALYs gained often depends on factors such as the youth of the patient. Using strict QALY criteria, many compassionate activities—end of life care, for example—would be deemed worthless. What escapes this type of measurement is that the value of one month lived well at the end of a person’s life may be vastly greater than the value of a month during the same person’s youth. And those suffering from rare and difficult conditions are likely to be ignored because they are expensice. So hidden inequalities emerge.

QALYs can measure health, as Tim shows, but it’s harder to measure social outcomes because they vary so widely. How does a regular donor compare health outcomes with social outcomes, such as getting a job or staying out of prison?

Although QALYs are a standard economic measure, not everyone agrees they are the right measure of health. How they are derived is contentious— for example many disabled people understandably take issue with the assumption made by QALYs that because of their impairments, the lives of people living with a disability must be of lower quality and are therefore less valuable.

Tim allows a personal bent towards economic reasoning reduce what is a very worthy question (how can I have the most impact?) to one component part. I’m glad he urges listeners to think about the worthiness of a cause before they donate, and advocate cost effectiveness too, but within each given context.

If every giving decision was carried to the same ‘logical conclusion’—in this case, that all donations should go to organisations working in the poorest parts of the world, where small amounts of money go far—then certainly nothing at all would go towards finding a cure or alleviating motor neurone disease.

Who is all this impact measurement really for? Find out the answer and understand how measurement informs accountability and power at the UK's annual social investment conference, Good Deals. This year the theme is Playtime's over – and when it comes to impact measurement it's all about moving past nice stories of impact to genuine accountability.