Size matters.

Just not when it comes to your yard. Indeed, “the size of new homes has been growing for decades now, but it’s coming at the expense of yard space,” concludes a new study, entitled “The Incredible Shrinking Yard,” released Wednesday by real estate firm Trulia.

The study found that homes built since 2015, on average, occupy 25% of the land on which they sit, while homes built in 1975 occupy just 13.9% and homes built back in the 1800s occupy less than 5% of their lots. Part of this is that lot sizes continue to shrink -- they’ve gotten 36.2% smaller in the past 40 years-- while home sizes have grown 15.2%.

While in the 1970s, the average home was about 1,800 square feet and the average lot size was 0.3 acres, nowadays those numbers are upwards of 2,000 square feet and just 0.2 acres. And in some cities, residents have barely any yard at all. In Miami and Oakland, for example, homes now take up about half of the lots they were built on, on average; when you consider that most homes have both a front and backyard, this often means just a tiny strip of green space, sometimes too little to even enjoy.

It’s unlikely we need all the extra space we’re now getting inside our homes -- at least if family size is any indication. The average family size has declined since the mid 1970s, according to data from the Pew Research Center -- as more families now opt for just one child. In 1976, 40% of mothers ages 40-44 had four or more children, compared to just 14% in 2014; meanwhile, just 11% of moms had one child in 1976, compared to 22% who did in 2014.

But we do need the yard space we’re now sacrificing, say psychologists. “A bigger home and smaller yard would encourage people to stay indoors, possibly focusing more on TV and social media,” says Jude Miller Burke, psychologist and psychologist and author of The Adversity Advantage: Turn Your Childhood Hardship into Career and Life Success. Both of those have been shown to have detrimental effects on our mental health: For example, the more time people spend on social media, the more likely they are to feel socially isolated.

“The visual beauty of grass and trees also encourages peacefulness and reflection, which is always good for the soul,” explains Miller Burke. And, as Los Angeles psychologist Crystal Lee points out “there is growing evidence that supports the benefits of being in or being exposed to nature.” Indeed, a Stanford study found that “walking in nature yields measurable mental benefits and may reduce risk of depression.” Other benefits of being in nature include anxiety and anger reduction.

Fran Walfish, a Beverly Hills psychotherapist and author of “The Self-Aware Parent,” points out that our children may be the biggest losers in the shrinking yard scenario. Having space to play in the yard allows them freedom from their parents and room to explore nature, she explains.

Of course, even larger homes on smaller lots often have ample yard space, and even if they don’t, there are other ways to get out into nature, including public parks. Still, there is “enormous value” in “sitting around a simple garden in the backyard sipping iced tea and relating to family members,” Walfish concludes.