If you want to be happy, don’t become a parent. Or, if you are a parent, just have one child. And wait until you’re older to have it. And have a job outside the home. And, if you can manage it, be a father instead of a mother.

That’s the collective advice of a slew of happiness studies conducted throughout the last decade.

If you want to be happy you should become a parent. Or if you’re already a parent, have more kids. When you are as young as possible. And stay at home with them. And, if you can manage it, be a mother instead of a father.

That’s also the collective advice of a slew of happiness studies conducted throughout the last decade.

Why are the findings of parental happiness studies so varied and often contradictory? Part of the problem is the incredibly broad term “happiness,” which is defined quite differently in different contexts. An even bigger problem is that, although, these studies use different methods for measuring happiness, news coverage of these studies often flattens their methodological differences.

A review paper can be a useful tool when researchers asking similar questions find different answers. Instead of conducting original research, authors of review studies try to understand how researchers tackling the same topic have come to different conclusions. Looking at review articles of parenting happiness can help us understand the limitations of happiness research, which can, in turn, help us make better sense of future findings.

Apples to oranges

In their 2014 Psychological Bulletin review article of parental happiness, authors Nelson, Kushlev, and Lyubomirsky describe the three basic methods used to measure happiness. The first method they identified was to make comparisons between parent and nonparent populations.

This type of study is like comparing apples to oranges. There is some value in comparing apples to oranges, as they are both parts of the larger category of “fruit.” Likewise, there is value to comparing parents to nonparents, as they are both parts of the larger category of “people.”

There are also limitations to this kind of comparison. For one thing, the labels of “parent” and “nonparent,” like their fruit counterparts, are broad categories. “Nonparent,” Nelson, Kuslev, and Lyubomirsky note, includes 20-year-olds who will eventually become parents, married couples who are struggling with infertility, and elderly couples who were childless by choice.

Those groups likely have completely different experiences and attitudes about children. “Parents” is just as broad a category, and both parents and nonparents have a host of confounding factors (age, gender, employment, etc.) that make comparisons difficult.

Even though both groups are broad categories, “parent” is a much larger group. The authors note that comparing parents to nonparents may be fraught because there are so many more parents than nonparents. Roughly 85% of Americans become parents, which means that at most, the “nonparent” category can include 15%. Because the members of that 15% are so different, it may be difficult to make large generalizations about them.

Observing apples as they ripen

A second way to study parental happiness is to collect data from people as they transition from being nonparents to being parents. We might say that, unlike studies comparing parents to nonparents (apples to oranges), these studies compare the apples as they ripen.

A benefit to this approach is that, because researchers are watching the same parents over time, the study has built-in controls for factors like age and gender.

A major limitation to these kinds of studies, the authors conclude, is time. They assert that the timetable of the studies in their review – about five years – may overstate the unhappiness of parents, based on factors related to early childhood. Like apples, early parenting has a relatively long shelf life, with parents reporting an initial surge of happiness. However, things start to sour once sleep deprivation sets in.

One major limitation of these “aging apple” studies is that researchers don’t keep following the apples. Fermented apple cider is not the same thing as an apple, but we might argue that it has been positively transformed as it ages. Such may be the case with parenting.

Comparing varieties of apples

A third way parental happiness is measured is having parents rank daily activities, like going to work, watching television, doing chores, working out, reading, and, of course, caring for children. In these types of studies, researchers examine the rankings to draw conclusions about parents’ happiness. Instead of comparing apples to oranges, or older apples to their younger selves, these studies are creating what amounts to a ranked list of apple varieties.

The rank-order used in such studies may make it seem like there are wide gaps between types of activities when those differences may not be statistically significant. One study in Nelson, Kushlev, and Lyubomirsky’s review ranked child care 12th out of 16 activities, while another ranked child care right in the middle at 9 out of 18. Some studies have found that rank order is significantly different for men and women, while others have not found such differences. Studies that rank parents’ most preferred activities may be artificially inflating the differences between them. A person might like Honeycrisp apples more than Gala apples, but that person generally likes apples.

Another problem with these types of studies is that they are less able to consider context. “Childcare” is almost as baggy a term as “happiness,” so what counts as childcare (changing diapers vs. play) may create bias. Even when broad terms like “childcare” are broken down into component tasks, it’s not clear how momentary enjoyment is linked to long-term satisfaction. A man may hate Granny Smith Apples on their own, but after the work of turning them into a pie, he might derive a lot of satisfaction from them. So parents who rank child care at the bottom of their day-to-day activities may find diapering, or potty training, or fighting over curfew to be extremely unpleasant tasks, but those tasks may have a long-term payoff.

Putting the “happiness gap” in perspective

Nelson, Kushlev, and Lyubomirsky’s review reminds us that no study can prove that apples are better than oranges. No individual study can definitively prove that parenting makes someone happy or unhappy, “because people cannot be randomly assigned to have or to forgo children, researchers cannot conclusively answer the causal question of whether parenthood improves well-being.”

A well-designed study, however, can highlight the possible disparities causing one group to report less happiness than another. The authors conclude that the best possible studies of parenting happiness would use a mix of the methodologies they describe, as such a hybrid design would help minimize the limitations associated with any one method.

Researchers could, for example, observe apples as they ripen (people as they transition to parenting) and oranges as they ripen (nonparents over the same period). Then they could compare the apples to the oranges.

Another hybrid design was used to find that the happiness gap between American parents and nonparents is wider than it is in any of 21 other countries. According to the study, American parents are less happy than American nonparents by a wider margin than any of the other countries studied (and in some of those countries, the gap is reversed, with parents being happier than nonparents).

This study benefits from more than one means of comparison. It begins by comparing apples to oranges (parents to nonparents), but then it compares its comparisons. Instead of just looking at American apples and American oranges, the compares the differences in American happiness to other countries.

That dual set of comparisons is the sort of mixed method approach suggested by Nelson, Kuslev, and Lyubomirsky’s review article. The researchers of the “happiness gap” study aren’t looking to declare parents happier than nonparents, but to determine what accounts for the wider gap between parent and nonparent happiness in some countries.

Their answer – the average cost of child care for a two-year-old and the number of paid sick leave days – suggests a new way of approaching the happiness gap. Instead of focusing on whether or not parents are happy, researchers could turn more productively to asking when and why parents are sometimes happier and sometimes unhappier than nonparents.

That also requires work from all of us, apples and oranges alike, to interrogate the claims behind the latest sensationalist headline and give weight to the humble review article.