One of the most difficult questions after a divorce is undoubtedly this: where should the children live? Is it better for them to divide their time between both parents? Or is it preferable for them to live primarily with one parent? For an individual family, this can be an almost impossible decision. More broadly, it is also a remarkably difficult question. Opinions are often shaped by personal experiences and deeply held beliefs. And the scientific evidence has not always been particularly clear either.

A new study by researchers from, among others, Yale, Duke, and Stockholm University now provides much stronger evidence for this sensitive and complex debate. The conclusion reached by Stella Canessa and a large team of colleagues appears relatively clear: for most families in their study, joint custody seems to produce better outcomes than arrangements in which children primarily live with just one parent. But, as always, it is worth reading beyond the headline.

Not as simple as it sounds

Studying this question is much harder than it first appears. Families who end up with joint custody often differ from those who do not long before the divorce takes place. Perhaps the parents communicate better, experience less conflict, or have different financial circumstances. Simply comparing these groups tells us very little because any differences might reflect those pre-existing characteristics rather than the custody arrangement itself.

The researchers therefore came up with an ingenious solution. They collected more than 25 years of Swedish court rulings on child custody and linked them to administrative records on income, education, and health. They then took advantage of an interesting feature of the Swedish legal system: custody cases are, in principle, assigned randomly to judges. However, some judges are much more likely than others to award joint custody. As a result, two otherwise very similar families can receive different custody arrangements simply because they happened to be assigned to different judges.

When I first read this, I admit I scratched my head a couple of times, wondering how luck can decide a whole life. But it is precisely this feature that makes the study methodologically much stronger than most previous research.

Fathers appear to benefit the most

The strongest effects were found for fathers. Fathers who were awarded joint custody earned more in the years following the divorce. Interestingly, the largest improvements were among fathers who would otherwise have been most likely to end up near the bottom of the income distribution. They also used substantially fewer antidepressants, suggesting better mental health.

The researchers argue that maintaining an active parental role may provide greater stability, a stronger sense of purpose, and perhaps more motivation to rebuild both work and family life. That is hardly a trivial finding.

Little changes for mothers

For mothers, the researchers found very few measurable effects. Their earnings did not change significantly, nor did they observe clear differences in mental health between the two custody arrangements.

This may sound surprising at first, but it is actually quite logical. In Sweden, when children primarily live with one parent after a separation, that parent is usually the mother. The transition from sole custody to joint custody therefore represents a much smaller change in day-to-day parenting than it does for fathers.

Children seem to benefit as well

Perhaps even more important for many readers are the findings for the children themselves.

Children in joint custody arrangements achieved higher scores on standardised school tests and were more likely to attend higher-performing schools. At the same time, the researchers found no evidence that either custody arrangement resulted in more serious mental health problems among children, measured through the use of antidepressants, anti-anxiety medication, or ADHD medication.

This is particularly relevant because one of the common concerns about joint custody is that moving between two homes may create additional stress for children. In this study, the researchers found no evidence supporting that concern.

But…

Does this mean that joint custody is always the best solution? That would be going too far.

First, this study was conducted in Sweden, a country with an extensive social safety net, widely available childcare, and a long tradition of active father involvement. The findings therefore cannot automatically be generalised to other countries.

Second, the estimated effects apply mainly to families whose custody outcome genuinely depended on which judge heard their case. Highly conflictual divorces or cases involving domestic violence largely fall outside these conclusions.

You may also have noticed that mental health was measured through prescription medication. That is a robust administrative measure, but it does not capture the full picture of well-being, stress, or happiness.

So?

This study certainly does not prove that joint custody is always the right answer. Family breakdown is rarely that simple, and I know all too well that every case is different. What this study does show, however, is that when circumstances allow it, joint custody may offer more benefits than many people have long assumed.