In "Why Aging and Working Makes us Happy in 4 Charts," Carol Graham describes a research paper in which she and co-author Milena Nikolova examine determinants of subjective well-being beyond traditional income measures. One of these is the relationship between age and happiness, a chart of which resembles, remarkably, a smile.

As Graham notes:

There is a U-shaped curve, with the low point in happiness being at roughly age 40 around the world, with some modest differences across countries. It seems that our veneration of (or for some of us, nostalgia, for) youth as the happiest times of our lives is overblown, the middle age years are, well, as expected, and then things get better as we age, as long as we are reasonably healthy (age-adjusted) and in a stable partnership.

The new post has three additional charts that showcase other ways to think about factors of happiness.

Feminism needs fathers. Unless and until men and women share the responsibilities of parenting equally, gender parity in the labor market will remain out of reach.

As Isabel Sawhill and I argued in our piece on “Men’s Lib” for the New York Times, “The gender revolution has been a one-sided effort. We have not pushed hard enough to put men in traditionally female roles—that is where our priority should lie now.”

An important step towards gender equality is then the provision of paternity leave, or at least forms of parental leave that can be taken up by fathers as well as mothers. Right now the U.S. is one of the few advanced nations with no dedicated leave for fathers:

But there are reasons to be hopeful. More companies are offering paternity leave or, like Amazon, a “leave bank” that parents can share between them. Hillary Clinton is promising to push for paid family leave if she wins in November. Recent studies of California’s paid leave scheme, introduced in 2004, suggest that there are significant benefits for fathers.

The number of fathers taking leave while the mother is in paid work rose by 50 percent, according to an analysis of the American Community Survey by Ann Bartel of Colombia and her colleagues.

Fathers of sons are more likely to take leave than those with daughters, suggesting that parents particularly value father-son bonding. Fathers were also very much more likely to take leave if they worked in occupations with a high share of female workers, indicating that workplace culture is also a big factor.

Men are more likely to take leave when it is exclusively available to them—with a so-called “use it or lose it” design—and when the period of leave is paid. The Quebec Parental Insurance Plan, for instance, which offers fathers three to five weeks at home with a child, resulted in a 250 percent increase father’s participation in parental leave.

Of course, there are costs. Paid leave has to be funded: either through payroll taxes (as most Democrats including Senator Kirsten Gillibrand want), taxes on the wealthy (Clinton’s preferred approach), or tax breaks for firms (as Marco Rubio has suggested).

So what are the upsides? Among the potential benefits from paternity leave are:

• A more equal division of labor in terms of parenting and childcare
• More equal sharing of domestic labor, including housework
• Less stress on the family
• Closer father-infant bonding
• Higher pay for mothers (according to a study in Sweden, future income for new mothers rises by 7 percent on average for every month of paternity leave taken by the father)

Gender roles have evolved rapidly in recent decades, especially in terms of the place and status of women. But the evolution of our mental models of masculinity, and especially fatherhood, has been slower. Helping fathers to take time to care for their children will help children, families, and women. Fathers need more than a day.

Paid leave for parents is likely to be an important issue on the campaign trail this year. Hillary Clinton, positioning herself as the candidate on the side of families, argues for all parents to be paid for 12 weeks of family leave, at two-thirds of their salary up to a (so far unspecified) cap. Donald Trump has not so far ruled it out, simply saying: “We have to keep our country very competitive, so you have to be careful of it.”

Polls routinely show high levels of general support for paid leave across the political spectrum. But there are many nuances here, including how to fund the leave entitlement, how long the leave should be, and whether fathers and mothers ought to get the same treatment.

Some light can be thrown on these questions by an analysis of the American Family Survey conducted earlier this year by Deseret News and the Center for the Study of Elections and Democracy (disclosure: I am an adviser to the pollsters). 

Views differ over the optimum length of leave depending on whether it is for the mother or father, and whether it is paid or unpaid:

But even Republicans are quite supportive, backing almost four months of paid leave for mothers and three months for fathers. So on the face of it, Clinton’s plan should be a vote winner even among moderate Republicans.

There are important implications about gender roles here. Encouraging men to take paid leave is important not only for the quality of family life, but also for gender equality more generally. Attitudes towards the role of fathers are shifting, although the primacy of motherhood remains. Among every ideological group there was greater support for longer maternity than paternity leave. It is worth noting, however, that half the respondents supported equal leave for mothers and fathers; the variation is driven by those in the other half, who drew a distinction by gender.

It turns out that the order in which the question is asked also makes a difference. For half the respondents, the question about maternity leave came before the one on paternity leave. For the other half, the questions were asked in the opposite order. (Because of the design of the survey, respondents could not change their previous answer.) The ordering of the question had an influence on responses:

Among those who gave an answer on paternity leave first, the gap between the preferred length of leave for mothers and fathers was much less. This was especially true for unpaid leave.

When people think about paid parental leave, many may think automatically of a mother, just as they think of a man when asked to picture a “strong leader.” Asking about maternity leave first goes with the traditional cultural grain, and results in more support for mothers compared to fathers. Asking about paternity leave first interrupts the normal gender framing, and narrows the gap.

There has been a slow revolution in attitudes towards the respective roles of mothers and fathers, reflected in the strongly symmetrical attitudes towards maternity and paternity leave in this survey. But there is more work to do. Mothers and fathers both need help balancing paid work and family life. Let’s hope this can be at least one area of agreement between Clinton and Trump.

The U.S. is the only advanced country without a paid leave policy, enabling workers to take time off to care for a new baby or other family member. At least two Presidential candidates, Hillary Clinton and Marco Rubio, have been talking about it, making it likely that it will get attention in 2016.

The idea has broad appeal now that most two-parent families and almost all one-parent families struggle with balancing work and family. Polls show that it is favored by 81 percent of the public—94 percent of Democrats, 80 percent of Independents and 65 percent of Republicans. Three states, California, New Jersey, and Rhode Island, have each enacted policies that could become models for other states or for the nation.

Paid leave promotes inclusive growth

Overall, paid leave is good for workers, good for children, and possibly even good for employers because of its role in helping to retain workers. It is also a policy that encourages inclusive growth. Studies of European systems suggest that paid leave increases female labor force participation and that the lack of it in the U.S. may be one reason for the decline in female labor force participation since 2000 and the growing female participation gap between the U.S. and other countries, adversely affecting our absolute and relative growth. The policy would make growth more inclusive because it would disproportionately benefit lower-wage workers.

The devil is in the design

The major issues in designing a paid leave policy are:

1. Eligibility, and especially the extent of work experience required to qualify (often a year);
2. the amount of leave allowed (Clinton suggests three months; Rubio four weeks);
3. the wage replacement rate (often two-thirds of regular wages up to a cap), and
4. financing.

Legislation proposed by Rep. Rosa DeLauro (D-CT) and Sen. Kirsten Gillibrand (D-NY) calls for a 0.2 percent payroll tax on employers and employees. Most states have made paid leave a part of their temporary disability systems. Senator Rubio proposes to finance it through a new tax credit for employers. 

Getting it right on eligibility, length of leave, and size of benefit

My own view is that a significant period of work experience should be required for eligibility to encourage stable employment before the birth of a child. This would not only encourage work but also insure that the subsidy was an earned benefit and not welfare by another name (but see below on financing).   

Leave periods need to be long enough to enable parents to bond with a child during the child’s first year of life but not so long that they lead to skill depreciation and to parents dropping out of the labor force. Three months seems like a good first step although it is far less generous than what many European countries provide (an average of 14 months across the OECD). That said, the Europeans may have gone too far. While there is little evidence that a leave as long as 6 months would have adverse effects on employment, when Canada extended their leave from six months to a year, the proportion of women returning to work declined.

A replacement rate of two-thirds up to a cap also seems reasonable although a higher replacement rate is one way to encourage more parents to take the leave. Among other things, more generous policies would have positive effects on the health and well-being of children. They might also encourage more fathers to take leave.  

How to pay for it

On financing, social insurance is the appropriate way to share the putative burden between employers and employees and avoid the stigma and unpopularity of social welfare. It would, in essence, change the default for employees (who are otherwise unlikely to save for purposes of taking leave). Some may worry that imposing any new costs on employers will lead to fewer employment opportunities. However, many economists believe that the employer portion of the tax is largely borne by workers in the form of lower wages. Moreover, in a study of 253 employers in California, over 90 percent reported either positive or no negative effects on profitability, turnover, and employee morale. Reductions in turnover, in particular, are noteworthy since turnover is a major expense for most employers. 

Will paid leave cause discrimination against women?

Another worry is discrimination against women. Here there is some cause for concern unless efforts are made to insure that leave is equally available to, and also used by, both men and women. This concern has led some countries to establish a use-it-or-lose-it set aside for fathers. In the province of Quebec, the proportion of fathers taking leave after implementation of such a policy increased from 21 to 75 percent and even after the leave period was over, men continued to share more equally in the care of their children.

Will Congress enact a national paid leave policy in the next few years? That’s doubtful in our current political environment but states may continue to take the lead. In the meantime, it can’t hurt if the major candidates are talking about the issue on the campaign trail.       

The issue of paid leave is heating up in 2016. At least two presidential candidates — Democrat Hillary Clinton and Republican Sen. Marco Rubio (Fla.) — have proposed new federal policies. Several states and large cities have begun providing paid leave to workers when they are ill or have to care for a newborn child or other family member.

This forward movement on paid-leave policy makes sense. The United States is the only advanced country without a paid-leave policy. While some private and public employers already provide paid leave to their workers, the workers least likely to get paid leave are low-wage and low-income workers who need it most. They also cannot afford to take unpaid leave, which the federal government mandates for larger companies.

Paid leave is good for the health and development of children; it supports work, enabling employees to remain attached to the labor force when they must take leave; and it can lower costly worker turnover for employers. Given the economic and social benefits it provides and given that the private market will not generate as much as needed, public policies should ensure that such leave is available to all.

But it is important to do so efficiently, so as not to burden employers with high costs that could lead them to substantially lower wages or create fewer jobs.

States and cities that require employers to provide paid sick days mandate just a small number, usually three to seven days. Family or temporary disability leaves that must be longer are usually financed through small increases in payroll taxes paid by workers and employers, rather than by employer mandates or general revenue.

Policy choices could limit costs while expanding benefits. For instance, states should limit eligibility to workers with experience, such as a year, and it might make sense to increase the benefit with years of accrued service to encourage labor force attachment. Some states provide four to six weeks of family leave, though somewhat larger amounts of time may be warranted, especially for the care of newborns, where three months seems reasonable.

Paid leave need not mean full replacement of existing wages. Replacing two-thirds of weekly earnings up to a set limit is reasonable. The caps and partial wage replacement give workers some incentive to limit their use of paid leave without imposing large financial burdens on those who need it most.

While many states and localities have made sensible choices in these areas, some have not. For instance, the D.C. Council has proposed paid-leave legislation for all but federal workers that violates virtually all of these rules. It would require up to 16 weeks of temporary disability leave and up to 16 weeks of paid family leave; almost all workers would be eligible for coverage, without major experience requirements; and the proposed law would require 100 percent replacement of wages up to $1,000 per week, and 50 percent coverage up to $3,000. It would be financed through a progressive payroll tax on employers only, which would increase to 1 percent for higher-paid employees.

Our analysis suggests that this level of leave would be badly underfunded by the proposed tax, perhaps by as much as two-thirds. Economists believe that payroll taxes on employers are mostly paid through lower worker wages, so the higher taxes needed to fully fund such generous leave would burden workers. The costly policy might cause employers to discriminate against women.

The disruptions and burdens of such lengthy leaves could cause employers to hire fewer workers or shift operations elsewhere over time. This is particularly true here, considering that the D.C. Council already has imposed costly burdens on employers, such as high minimum wages (rising to $11.50 per hour this year), paid sick leave (although smaller amounts than now proposed) and restrictions on screening candidates. The minimum wage in Arlington is $7.25 with no other mandates. Employers will be tempted to move operations across the river or to replace workers with technology wherever possible.

Cities, states and the federal government should provide paid sick and family leave for all workers. But it can and should be done in a fiscally responsible manner that does not place undue burdens on the workers themselves or on their employers.

Editor's note: this piece originally appeared in The Washington Post.