The United States is the most powerful colossus in the history of the world: Our nuclear warheads could wipe out the globe, our enemies tweet on iPhones, and kids worldwide bop to Beyonce.

Yet let’s get real. All this hasn’t benefited all Americans. A newly released global index finds that America falls short, along with other powerful countries, on what matters most: assuring a high quality of life for ordinary citizens.

The Social Progress Index for 2015 ranks the United States 16th in the world. We may thump our chests and boast that we’re No. 1, and in some ways we are. But, in important ways, we lag.

The index ranks the United States 30th in life expectancy, 38th in saving children’s lives, and a humiliating 55th in women surviving childbirth. O.K., we know that we have a high homicide rate, but we’re at risk in other ways as well. We have higher traffic fatality rates than 37 other countries, and higher suicide rates than 80.

We also rank 32nd in preventing early marriage, 38th in the equality of our education system, 49th in high school enrollment rates and 87th in cellphone use.

Ouch. “We’re No. 87!” doesn’t have much of a ring to it, does it?

Michael E. Porter, the Harvard Business School professor who helped devise the Social Progress Index, says that it’s important to have conventional economic measures such as G.D.P. growth. But social progress is also a critical measure, he notes, of how a country is serving its people.

“We’re not now No. 1 in a lot of stuff that traditionally we have been,” said Professor Porter, an expert on international competitiveness. “What we’re learning is that the fact that we’re not No. 1 on this stuff also means that we’re facing long-term economic stresses.”

“We’re starting to understand that we can’t put economic development and social progress in two separate buckets,” Porter added. “There’s a dialectic here.”

The top countries in the 2015 Social Progress Index are Norway, Sweden, Switzerland, Iceland, New Zealand and Canada. Of the 133 countries rated, Central African Republic is last, just after Chad and Afghanistan.

Sri Lanka does better than India. Bangladesh outperforms Pakistan. Both the Philippines and South Africa do better than Russia. Mongolia comes in ahead of China. And Canada wallops the United States.

One way of looking at the index is to learn from countries that outperform by having social indicators better than their income levels. By that standard, the biggest stars are Costa Rica and Uruguay, with New Zealand and Rwanda also outperforming.

“This takes time,” said Michael Green, executive director of the Social Progress Imperative, which produces the index. “Costa Rica is an overperformer because of its history.”

Green notes that Costa Rica offered free, universal primary education in the 19th century. In the 20th century, it disbanded its military forces and invested some of the savings in education. One payoff: Some surveys have found Costa Ricans among the happiest people in the world.

Then there are the underperformers that do worse than would be expected from their income level. Saudi Arabia leads that list.

The Social Progress Index, now in its second year, might seem a clarion call for greater equality, but that’s not quite right. Professor Porter and his number-crunchers found only a mild correlation between economic equality (measured by Gini coefficient) and social progress. What mattered much more was poverty.

Of course, wealthy countries with high poverty tend to be unequal as well. But inequality at the top seems to matter less for well-being than inequality at the bottom. Perhaps we should worry less about reining in the top 1 percent and more about helping the bottom 20 percent?

On the other hand, one way to finance empowerment programs is to raise taxes on tycoons. And when there is tremendous inequality, the wealthy create private alternatives to public goods . private schools, private security forces, gated communities . that lead to disinvestment in public goods vital to the needy.

In any case, the 2015 Social Progress Index should serve notice to Americans . and to people around the globe. We obsess on the wrong measures, so we often have the wrong priorities.

As an American, what saddens me is also that our political system seems unable to rise to the challenges.

As Porter notes, Americans generally understand that we face economic impediments such as declining infrastructure, yet we’re frozen. We appreciate that our education system is a mess, yet we’re passive.

We can send people to space and turn watches into computers, but we seem incapable of consensus on the issues that matter most to our children . so our political system remains in gridlock, even as other countries pass us by.