If Taylor Swift - the poster girl for casting your 20s friendship net far and wide with her ever-expanding squad - causes you anxiety over the size of your social group, you can stop worrying once you've hit 30.

Research indicates that happiness beyond the big 3-0 is related to the friendships you have when younger, and while the quantity of friends in your 20s is important, in your 30s it's the quality that matters.

The study, led by Cheryl L. Carmichael and published in the journal Psychology and Aging, used data from 200 university students who kept diaries tracking the frequency and intimacy of their social interactions for two weeks at the age of around 20 and another two weeks at around 30, rating the pleasantness of each interaction.

Then in 2007/08, at age 50, just over 100 of the subjects were tested for “psychosocial outcomes (social integration, friendship quality, loneliness, depression, and psychological well-being)”.

Researchers found that plenty of socialising in their 20s had a positive effect on the participants' wellbeing later in life, but in their 30s, it was the quality of the socialising rather than the amount that had a positive effect.

The report says: “Results supported the hypothesis that the quantity (but not the quality) of social interactions at age 20, and the quality (but not the quantity) of social interactions at age 30 predict midlife psychosocial outcomes [...] age-20 interaction quantity had a direct, unmediated effect on age-50 social and psychological outcomes.

“The effects of age-20 interaction quality on midlife outcomes, on the other hand, were mediated by age-30 interaction quality. Our findings are consistent with the idea that selection and optimization serve important functions in early adulthood”.

Those behind the study suggest the traditional changes in life in your 30s, such as families and careers, affect how much time you have to spend with friends, thus leaving the ones who matter.

Carmichael acknowledges that those tested were in their 30s in the 1980's, and these days those life events may unfold at a later age.

However, friendship changes could also be down to simply having a stronger sense of identity in your 30s than your 20s, meaning you're not necessarily as open to new social groups, regardless of children and work.

Carmichael says: “As individuals approach their 30s, social information-seeking motives wane [...] Identity exploration goals diminish with the transition into better-defined and more enduring social roles.”

As NYmag.com points out, these days we have the added complication of social media keeping us in contact with friends from years gone by providing a wealth of daily interactions the study's participants didn't have access to.

However, a ‘like’ on a profile picture does not a BFF make - it's the people you'd call first with the good and the bad who matter. And science concurs - quality over quantity makes for a more fulfilled life. Do you agree?

Words: Amy Swales / Images: Rex Features, @taylorswift