The metaphor that "a rising tide lifts all boats" was popularized by President John F. Kennedy, who borrowed the phrase to defend a controversial public works project. There is some truth in it.
When an economy is growing strongly, the chances for improved conditions for nearly any group in society improve. But not all groups become better off at the same rate, and a few miss out entirely.
When economic tides go out as a result of a recession or financial crisis, not every "ship" sinks to the same level or goes aground as soon as others. And although some craft go aground on soft sand to refloat again, others are dashed against the rocks and sink for good.
That certainly has been true in the aftermath of the financial debacle that began to unfold six years ago, according to two St. Louis Federal Reserve Bank researchers, William Emmons and Bryan Noeth.
In one report, they describe how baby boomers, those born from 1946 through 1964, and Generation Xers, typically born from 1965 through 1982, have fared worse than the generations preceding them in terms of real incomes and net worth.
In another study, they note that young families, those headed by someone younger than 40, lost proportionately much more net worth from 2007 to 2010 than ones with middle-age heads of households ages 40 through 61 or households of those 62 and older.
The reports by Emmons and Noeth hark back to that of the University of Southern California's Richard Easterlin, whose pathbreaking 1980 book "Birth and Fortune" examined the relationship between when people are born and how much income and wealth they enjoy over their lifetimes.
Easterlin focused on how the size of birth cohorts, which are groups born in particular periods, affects the labor supply at given points in time, and hence wage rates.
Many of the "Lucky Few," born between 1929 and 1945, experienced Depression-era poverty as tots and in early grade school. But they were the first U.S. age cohort that was smaller than the one preceding it. Prosperity arrived with the outbreak of war in Europe when the oldest were 10 years old.
Nearly all their working-age years were spent in eras of good economic growth. And the fact there were so few of them pushed up wage rates.
Baby boomers, the generation that followed, experienced the reverse: A burgeoning labor supply held down real wage growth. Plus, the increasing participation of women in the labor market, driven in part by changing social attitudes, accentuated this and partially resulted from it.
With stagnant wages, one-earner households could not achieve the same increases in standards of living as had the previous generation. Traditionally nonworking spouses had to get jobs, and this had a vicious-circle effect of further diluting the labor supply and suppressing wages.
Birth cohort size is not the only factor in how an age group fares.
If the overall economy is prosperous in your prime earning years, you generally will end up with higher real income and more net worth than someone whose prime earning years fall within a prolonged downturn.
The U.S. economy had a bad slump after the Panic of 1907, but was recovering well by 1910 and really took off with the outbreak of World War I in Europe in 1914. (The United States did very well economically in the 20th century by staying out of both world wars for two to three years, while selling goods to combatants at high prices.)
So there was a decade of solid prosperity that accorded long-run benefits to those ages 25 to 45 in the decade that began in 1910. They had better lifetime earnings than their children, who had a decade of earnings decimated by the Depression.
The same sorts of factors are in play now. Those 62 and older had two decades of solid earnings for their age groups prior to 2007. After full work careers, they had more assets, of which their houses were the largest component.
Although their net worth was exposed to drops in housing prices, they were not as leveraged as younger cohorts were, and particularly not as leveraged as those in their 20s and early 30s who had taken on much mortgage debt in anticipation of ever-rising house prices. That group has suffered the most.
As a group, those now older than 62 also were less exposed to layoffs, reduced hours or smaller commissions and bonuses than younger people since fewer of them still were in the labor force. They also were more diversified, with more assets in addition to their homes.
Within this pattern, there certainly are exceptions.
Many people in their early 60s expected to work for another five years or more at the best salary levels of their lives. Instead they were let go and forced into early retirement by their inability to get other jobs. This was at a time when, with kids already out of the house and college expenses in the past, they expected to be able to plow high proportions of earnings into retirement accounts.
At the other end of the labor force, those who graduated from college in 2008 later had a harder time gaining a toehold in the economy than those who hit the job market in the early 1990s. They rightly worry that when prosperity returns, their resumes, filled with years of low-skilled jobs, will compare unfavorably with those of fresh graduates five or 10 years younger.
Many other factors are at play. We are not out of the woods yet, and it isn't clear what the post-debacle global economy or even just that of our own country will look like.
So take the works of Emmons and Noeth as good first efforts to address a long-term issue.
Economist Edward Lotterman teaches and writes in St. Paul, Minn. Write him at email@example.com.