This is a worrying time for those who believe government policies should be based on the best evidence. Pundits claim we've entered a postfactual era. Viral fake news stories spread alternative facts. On some issues, such as climate change and childhood vaccinations, many scientists worry their hard-won research findings have lost sway with politicians and the public, and feel their veracity is under attack. Some are taking to the internet and even to the streets to speak up for evidence. But just how should evidence shape policy? And why does it sometimes lose out?
As this special section shows, evidence still plays a key role in the machinery of government, especially in the robust bureaucracies of the United States and Europe, where legal mandates often require the input of technical specialists. Many politicians and policy wonks also want to better understand the problems they are trying to solve, whether costly policy remedies will be effective, and whether taxpayers will get their money's worth. So they demand data as they make decisions on a wide range of issues, including how to regulate toxic chemicals, evaluate education programs, treat disease, and shape policies that can affect vast swaths of the economy and millions of people.
That doesn't mean the path of evidence to policy is straight, or that the evidence always determines the outcome. There's no question that carbon dioxide is building up in the atmosphere and before long will increase global temperatures by 2°C if emissions aren't curbed. But those numbers can't tell a policymaker whether the best way to limit warming is to impose a carbon tax, create an emissions trading system, enact a ban on fossil fuels, or simply do nothing and let the next generation figure it out.
That last idea might not be responsible, but it's a reminder that evidence is just one of many ingredients—along with economic concerns, religious views, and ideological perspectives on the role of government—that go into the policy mix. Even before "alternative facts" became a meme, belief and ideology sometimes trumped evidence, as when parents rejected vaccines for their children and politicians snubbed potentially life-saving interventions for drug abusers.
There are other complexities. Even in arenas where evidence is essential—such as deciding whether a drug is safe or how to regulate a pollutant—there can be honest disagreements about what kinds of evidence should be allowed into the process. All studies are not equal.
Then there is the problem of what policymakers should do when studies offer no clear-cut answer to the question at hand—or conflicting evidence. It's safe to say that, in many areas, more study is almost always needed. But what to do in a world where resources for more science are almost always limited, and decisions need to be made?
Veterans of the policy wars say such hurdles shouldn't prevent scientists from enlisting. But don't go unarmed. Learn the lingo, and identify the key players. Realize that the path of evidence is winding, and the destination often distant. It's not unusual for it to take decades for the weight of evidence to leave its mark on policy. But when it does, the results can often be extraordinary, saving millions of lives, and reminding people of the power of fact.